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Unlike map() and its variants which always return a fixed object type (list for map(), integer vector for map_int(), etc), the modify() family always returns the same type as the input object.

  • modify() is a shortcut for x[[i]] <- f(x[[i]]); return(x).

  • modify_if() only modifies the elements of x that satisfy a predicate and leaves the others unchanged. modify_at() only modifies elements given by names or positions.

  • modify2() modifies the elements of .x but also passes the elements of .y to .f, just like map2(). imodify() passes the names or the indices to .f like imap() does.

  • modify_in() modifies a single element in a pluck() location.

Usage

modify(.x, .f, ...)

modify_if(.x, .p, .f, ..., .else = NULL)

modify_at(.x, .at, .f, ...)

modify2(.x, .y, .f, ...)

imodify(.x, .f, ...)

Arguments

.x

A vector.

.f

A function specified in the same way as the corresponding map function.

...

Additional arguments passed on to the mapped function.

We now generally recommend against using ... to pass additional (constant) arguments to .f. Instead use a shorthand anonymous function:

# Instead of
x |> map(f, 1, 2, collapse = ",")
# do:
x |> map(\(x) f(x, 1, 2, collapse = ","))

This makes it easier to understand which arguments belong to which function and will tend to yield better error messages.

.p

A single predicate function, a formula describing such a predicate function, or a logical vector of the same length as .x. Alternatively, if the elements of .x are themselves lists of objects, a string indicating the name of a logical element in the inner lists. Only those elements where .p evaluates to TRUE will be modified.

.else

A function applied to elements of .x for which .p returns FALSE.

.at

A logical, integer, or character vector giving the elements to select. Alternatively, a function that takes a vector of names, and returns a logical, integer, or character vector of elements to select.

[Deprecated]: if the tidyselect package is installed, you can use vars() and tidyselect helpers to select elements.

.y

A vector, usually the same length as .x.

Value

An object the same class as .x

Details

Since the transformation can alter the structure of the input; it's your responsibility to ensure that the transformation produces a valid output. For example, if you're modifying a data frame, .f must preserve the length of the input.

Genericity

modify() and variants are generic over classes that implement length(), [[ and [[<- methods. If the default implementation is not compatible for your class, you can override them with your own methods.

If you implement your own modify() method, make sure it satisfies the following invariants:

modify(x, identity) === x
modify(x, compose(f, g)) === modify(x, g) |> modify(f)

These invariants are known as the functor laws in computer science.

See also

Other map variants: imap(), lmap(), map(), map2(), map_depth(), map_if(), pmap()

Other modify variants: map_depth(), modify_tree()

Examples

# Convert factors to characters
iris |>
  modify_if(is.factor, as.character) |>
  str()
#> 'data.frame':	150 obs. of  5 variables:
#>  $ Sepal.Length: num  5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ...
#>  $ Sepal.Width : num  3.5 3 3.2 3.1 3.6 3.9 3.4 3.4 2.9 3.1 ...
#>  $ Petal.Length: num  1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 ...
#>  $ Petal.Width : num  0.2 0.2 0.2 0.2 0.2 0.4 0.3 0.2 0.2 0.1 ...
#>  $ Species     : chr  "setosa" "setosa" "setosa" "setosa" ...

# Specify which columns to map with a numeric vector of positions:
mtcars |> modify_at(c(1, 4, 5), as.character) |> str()
#> 'data.frame':	32 obs. of  11 variables:
#>  $ mpg : chr  "21" "21" "22.8" "21.4" ...
#>  $ cyl : num  6 6 4 6 8 6 8 4 4 6 ...
#>  $ disp: num  160 160 108 258 360 ...
#>  $ hp  : chr  "110" "110" "93" "110" ...
#>  $ drat: chr  "3.9" "3.9" "3.85" "3.08" ...
#>  $ wt  : num  2.62 2.88 2.32 3.21 3.44 ...
#>  $ qsec: num  16.5 17 18.6 19.4 17 ...
#>  $ vs  : num  0 0 1 1 0 1 0 1 1 1 ...
#>  $ am  : num  1 1 1 0 0 0 0 0 0 0 ...
#>  $ gear: num  4 4 4 3 3 3 3 4 4 4 ...
#>  $ carb: num  4 4 1 1 2 1 4 2 2 4 ...

# Or with a vector of names:
mtcars |> modify_at(c("cyl", "am"), as.character) |> str()
#> 'data.frame':	32 obs. of  11 variables:
#>  $ mpg : num  21 21 22.8 21.4 18.7 18.1 14.3 24.4 22.8 19.2 ...
#>  $ cyl : chr  "6" "6" "4" "6" ...
#>  $ disp: num  160 160 108 258 360 ...
#>  $ hp  : num  110 110 93 110 175 105 245 62 95 123 ...
#>  $ drat: num  3.9 3.9 3.85 3.08 3.15 2.76 3.21 3.69 3.92 3.92 ...
#>  $ wt  : num  2.62 2.88 2.32 3.21 3.44 ...
#>  $ qsec: num  16.5 17 18.6 19.4 17 ...
#>  $ vs  : num  0 0 1 1 0 1 0 1 1 1 ...
#>  $ am  : chr  "1" "1" "1" "0" ...
#>  $ gear: num  4 4 4 3 3 3 3 4 4 4 ...
#>  $ carb: num  4 4 1 1 2 1 4 2 2 4 ...

list(x = sample(c(TRUE, FALSE), 100, replace = TRUE), y = 1:100) |>
  list_transpose(simplify = FALSE) |>
  modify_if("x", \(l) list(x = l$x, y = l$y * 100)) |>
  list_transpose()
#> $x
#>   [1]  TRUE  TRUE  TRUE FALSE  TRUE FALSE  TRUE FALSE  TRUE  TRUE FALSE
#>  [12]  TRUE  TRUE FALSE FALSE  TRUE FALSE  TRUE FALSE  TRUE FALSE FALSE
#>  [23] FALSE  TRUE FALSE FALSE FALSE FALSE FALSE  TRUE FALSE FALSE FALSE
#>  [34] FALSE  TRUE FALSE FALSE  TRUE FALSE  TRUE FALSE  TRUE  TRUE FALSE
#>  [45]  TRUE  TRUE FALSE FALSE FALSE FALSE FALSE  TRUE  TRUE FALSE FALSE
#>  [56]  TRUE FALSE FALSE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE FALSE FALSE
#>  [67] FALSE  TRUE FALSE  TRUE FALSE  TRUE  TRUE  TRUE FALSE FALSE  TRUE
#>  [78]  TRUE FALSE FALSE  TRUE  TRUE FALSE FALSE  TRUE FALSE  TRUE  TRUE
#>  [89]  TRUE  TRUE  TRUE FALSE FALSE  TRUE  TRUE  TRUE FALSE  TRUE  TRUE
#> [100] FALSE
#> 
#> $y
#>   [1]  100  200  300    4  500    6  700    8  900 1000   11 1200 1300
#>  [14]   14   15 1600   17 1800   19 2000   21   22   23 2400   25   26
#>  [27]   27   28   29 3000   31   32   33   34 3500   36   37 3800   39
#>  [40] 4000   41 4200 4300   44 4500 4600   47   48   49   50   51 5200
#>  [53] 5300   54   55 5600   57   58 5900 6000 6100 6200 6300   64   65
#>  [66]   66   67 6800   69 7000   71 7200 7300 7400   75   76 7700 7800
#>  [79]   79   80 8100 8200   83   84 8500   86 8700 8800 8900 9000 9100
#>  [92]   92   93 9400 9500 9600   97 9800 9900  100
#> 

# Use modify2() to map over two vectors and preserve the type of
# the first one:
x <- c(foo = 1L, bar = 2L)
y <- c(TRUE, FALSE)
modify2(x, y, \(x, cond) if (cond) x else 0L)
#> foo bar 
#>   1   0 

# Use a predicate function to decide whether to map a function:
modify_if(iris, is.factor, as.character)
#>     Sepal.Length Sepal.Width Petal.Length Petal.Width    Species
#> 1            5.1         3.5          1.4         0.2     setosa
#> 2            4.9         3.0          1.4         0.2     setosa
#> 3            4.7         3.2          1.3         0.2     setosa
#> 4            4.6         3.1          1.5         0.2     setosa
#> 5            5.0         3.6          1.4         0.2     setosa
#> 6            5.4         3.9          1.7         0.4     setosa
#> 7            4.6         3.4          1.4         0.3     setosa
#> 8            5.0         3.4          1.5         0.2     setosa
#> 9            4.4         2.9          1.4         0.2     setosa
#> 10           4.9         3.1          1.5         0.1     setosa
#> 11           5.4         3.7          1.5         0.2     setosa
#> 12           4.8         3.4          1.6         0.2     setosa
#> 13           4.8         3.0          1.4         0.1     setosa
#> 14           4.3         3.0          1.1         0.1     setosa
#> 15           5.8         4.0          1.2         0.2     setosa
#> 16           5.7         4.4          1.5         0.4     setosa
#> 17           5.4         3.9          1.3         0.4     setosa
#> 18           5.1         3.5          1.4         0.3     setosa
#> 19           5.7         3.8          1.7         0.3     setosa
#> 20           5.1         3.8          1.5         0.3     setosa
#> 21           5.4         3.4          1.7         0.2     setosa
#> 22           5.1         3.7          1.5         0.4     setosa
#> 23           4.6         3.6          1.0         0.2     setosa
#> 24           5.1         3.3          1.7         0.5     setosa
#> 25           4.8         3.4          1.9         0.2     setosa
#> 26           5.0         3.0          1.6         0.2     setosa
#> 27           5.0         3.4          1.6         0.4     setosa
#> 28           5.2         3.5          1.5         0.2     setosa
#> 29           5.2         3.4          1.4         0.2     setosa
#> 30           4.7         3.2          1.6         0.2     setosa
#> 31           4.8         3.1          1.6         0.2     setosa
#> 32           5.4         3.4          1.5         0.4     setosa
#> 33           5.2         4.1          1.5         0.1     setosa
#> 34           5.5         4.2          1.4         0.2     setosa
#> 35           4.9         3.1          1.5         0.2     setosa
#> 36           5.0         3.2          1.2         0.2     setosa
#> 37           5.5         3.5          1.3         0.2     setosa
#> 38           4.9         3.6          1.4         0.1     setosa
#> 39           4.4         3.0          1.3         0.2     setosa
#> 40           5.1         3.4          1.5         0.2     setosa
#> 41           5.0         3.5          1.3         0.3     setosa
#> 42           4.5         2.3          1.3         0.3     setosa
#> 43           4.4         3.2          1.3         0.2     setosa
#> 44           5.0         3.5          1.6         0.6     setosa
#> 45           5.1         3.8          1.9         0.4     setosa
#> 46           4.8         3.0          1.4         0.3     setosa
#> 47           5.1         3.8          1.6         0.2     setosa
#> 48           4.6         3.2          1.4         0.2     setosa
#> 49           5.3         3.7          1.5         0.2     setosa
#> 50           5.0         3.3          1.4         0.2     setosa
#> 51           7.0         3.2          4.7         1.4 versicolor
#> 52           6.4         3.2          4.5         1.5 versicolor
#> 53           6.9         3.1          4.9         1.5 versicolor
#> 54           5.5         2.3          4.0         1.3 versicolor
#> 55           6.5         2.8          4.6         1.5 versicolor
#> 56           5.7         2.8          4.5         1.3 versicolor
#> 57           6.3         3.3          4.7         1.6 versicolor
#> 58           4.9         2.4          3.3         1.0 versicolor
#> 59           6.6         2.9          4.6         1.3 versicolor
#> 60           5.2         2.7          3.9         1.4 versicolor
#> 61           5.0         2.0          3.5         1.0 versicolor
#> 62           5.9         3.0          4.2         1.5 versicolor
#> 63           6.0         2.2          4.0         1.0 versicolor
#> 64           6.1         2.9          4.7         1.4 versicolor
#> 65           5.6         2.9          3.6         1.3 versicolor
#> 66           6.7         3.1          4.4         1.4 versicolor
#> 67           5.6         3.0          4.5         1.5 versicolor
#> 68           5.8         2.7          4.1         1.0 versicolor
#> 69           6.2         2.2          4.5         1.5 versicolor
#> 70           5.6         2.5          3.9         1.1 versicolor
#> 71           5.9         3.2          4.8         1.8 versicolor
#> 72           6.1         2.8          4.0         1.3 versicolor
#> 73           6.3         2.5          4.9         1.5 versicolor
#> 74           6.1         2.8          4.7         1.2 versicolor
#> 75           6.4         2.9          4.3         1.3 versicolor
#> 76           6.6         3.0          4.4         1.4 versicolor
#> 77           6.8         2.8          4.8         1.4 versicolor
#> 78           6.7         3.0          5.0         1.7 versicolor
#> 79           6.0         2.9          4.5         1.5 versicolor
#> 80           5.7         2.6          3.5         1.0 versicolor
#> 81           5.5         2.4          3.8         1.1 versicolor
#> 82           5.5         2.4          3.7         1.0 versicolor
#> 83           5.8         2.7          3.9         1.2 versicolor
#> 84           6.0         2.7          5.1         1.6 versicolor
#> 85           5.4         3.0          4.5         1.5 versicolor
#> 86           6.0         3.4          4.5         1.6 versicolor
#> 87           6.7         3.1          4.7         1.5 versicolor
#> 88           6.3         2.3          4.4         1.3 versicolor
#> 89           5.6         3.0          4.1         1.3 versicolor
#> 90           5.5         2.5          4.0         1.3 versicolor
#> 91           5.5         2.6          4.4         1.2 versicolor
#> 92           6.1         3.0          4.6         1.4 versicolor
#> 93           5.8         2.6          4.0         1.2 versicolor
#> 94           5.0         2.3          3.3         1.0 versicolor
#> 95           5.6         2.7          4.2         1.3 versicolor
#> 96           5.7         3.0          4.2         1.2 versicolor
#> 97           5.7         2.9          4.2         1.3 versicolor
#> 98           6.2         2.9          4.3         1.3 versicolor
#> 99           5.1         2.5          3.0         1.1 versicolor
#> 100          5.7         2.8          4.1         1.3 versicolor
#> 101          6.3         3.3          6.0         2.5  virginica
#> 102          5.8         2.7          5.1         1.9  virginica
#> 103          7.1         3.0          5.9         2.1  virginica
#> 104          6.3         2.9          5.6         1.8  virginica
#> 105          6.5         3.0          5.8         2.2  virginica
#> 106          7.6         3.0          6.6         2.1  virginica
#> 107          4.9         2.5          4.5         1.7  virginica
#> 108          7.3         2.9          6.3         1.8  virginica
#> 109          6.7         2.5          5.8         1.8  virginica
#> 110          7.2         3.6          6.1         2.5  virginica
#> 111          6.5         3.2          5.1         2.0  virginica
#> 112          6.4         2.7          5.3         1.9  virginica
#> 113          6.8         3.0          5.5         2.1  virginica
#> 114          5.7         2.5          5.0         2.0  virginica
#> 115          5.8         2.8          5.1         2.4  virginica
#> 116          6.4         3.2          5.3         2.3  virginica
#> 117          6.5         3.0          5.5         1.8  virginica
#> 118          7.7         3.8          6.7         2.2  virginica
#> 119          7.7         2.6          6.9         2.3  virginica
#> 120          6.0         2.2          5.0         1.5  virginica
#> 121          6.9         3.2          5.7         2.3  virginica
#> 122          5.6         2.8          4.9         2.0  virginica
#> 123          7.7         2.8          6.7         2.0  virginica
#> 124          6.3         2.7          4.9         1.8  virginica
#> 125          6.7         3.3          5.7         2.1  virginica
#> 126          7.2         3.2          6.0         1.8  virginica
#> 127          6.2         2.8          4.8         1.8  virginica
#> 128          6.1         3.0          4.9         1.8  virginica
#> 129          6.4         2.8          5.6         2.1  virginica
#> 130          7.2         3.0          5.8         1.6  virginica
#> 131          7.4         2.8          6.1         1.9  virginica
#> 132          7.9         3.8          6.4         2.0  virginica
#> 133          6.4         2.8          5.6         2.2  virginica
#> 134          6.3         2.8          5.1         1.5  virginica
#> 135          6.1         2.6          5.6         1.4  virginica
#> 136          7.7         3.0          6.1         2.3  virginica
#> 137          6.3         3.4          5.6         2.4  virginica
#> 138          6.4         3.1          5.5         1.8  virginica
#> 139          6.0         3.0          4.8         1.8  virginica
#> 140          6.9         3.1          5.4         2.1  virginica
#> 141          6.7         3.1          5.6         2.4  virginica
#> 142          6.9         3.1          5.1         2.3  virginica
#> 143          5.8         2.7          5.1         1.9  virginica
#> 144          6.8         3.2          5.9         2.3  virginica
#> 145          6.7         3.3          5.7         2.5  virginica
#> 146          6.7         3.0          5.2         2.3  virginica
#> 147          6.3         2.5          5.0         1.9  virginica
#> 148          6.5         3.0          5.2         2.0  virginica
#> 149          6.2         3.4          5.4         2.3  virginica
#> 150          5.9         3.0          5.1         1.8  virginica

# Specify an alternative with the `.else` argument:
modify_if(iris, is.factor, as.character, .else = as.integer)
#>     Sepal.Length Sepal.Width Petal.Length Petal.Width    Species
#> 1              5           3            1           0     setosa
#> 2              4           3            1           0     setosa
#> 3              4           3            1           0     setosa
#> 4              4           3            1           0     setosa
#> 5              5           3            1           0     setosa
#> 6              5           3            1           0     setosa
#> 7              4           3            1           0     setosa
#> 8              5           3            1           0     setosa
#> 9              4           2            1           0     setosa
#> 10             4           3            1           0     setosa
#> 11             5           3            1           0     setosa
#> 12             4           3            1           0     setosa
#> 13             4           3            1           0     setosa
#> 14             4           3            1           0     setosa
#> 15             5           4            1           0     setosa
#> 16             5           4            1           0     setosa
#> 17             5           3            1           0     setosa
#> 18             5           3            1           0     setosa
#> 19             5           3            1           0     setosa
#> 20             5           3            1           0     setosa
#> 21             5           3            1           0     setosa
#> 22             5           3            1           0     setosa
#> 23             4           3            1           0     setosa
#> 24             5           3            1           0     setosa
#> 25             4           3            1           0     setosa
#> 26             5           3            1           0     setosa
#> 27             5           3            1           0     setosa
#> 28             5           3            1           0     setosa
#> 29             5           3            1           0     setosa
#> 30             4           3            1           0     setosa
#> 31             4           3            1           0     setosa
#> 32             5           3            1           0     setosa
#> 33             5           4            1           0     setosa
#> 34             5           4            1           0     setosa
#> 35             4           3            1           0     setosa
#> 36             5           3            1           0     setosa
#> 37             5           3            1           0     setosa
#> 38             4           3            1           0     setosa
#> 39             4           3            1           0     setosa
#> 40             5           3            1           0     setosa
#> 41             5           3            1           0     setosa
#> 42             4           2            1           0     setosa
#> 43             4           3            1           0     setosa
#> 44             5           3            1           0     setosa
#> 45             5           3            1           0     setosa
#> 46             4           3            1           0     setosa
#> 47             5           3            1           0     setosa
#> 48             4           3            1           0     setosa
#> 49             5           3            1           0     setosa
#> 50             5           3            1           0     setosa
#> 51             7           3            4           1 versicolor
#> 52             6           3            4           1 versicolor
#> 53             6           3            4           1 versicolor
#> 54             5           2            4           1 versicolor
#> 55             6           2            4           1 versicolor
#> 56             5           2            4           1 versicolor
#> 57             6           3            4           1 versicolor
#> 58             4           2            3           1 versicolor
#> 59             6           2            4           1 versicolor
#> 60             5           2            3           1 versicolor
#> 61             5           2            3           1 versicolor
#> 62             5           3            4           1 versicolor
#> 63             6           2            4           1 versicolor
#> 64             6           2            4           1 versicolor
#> 65             5           2            3           1 versicolor
#> 66             6           3            4           1 versicolor
#> 67             5           3            4           1 versicolor
#> 68             5           2            4           1 versicolor
#> 69             6           2            4           1 versicolor
#> 70             5           2            3           1 versicolor
#> 71             5           3            4           1 versicolor
#> 72             6           2            4           1 versicolor
#> 73             6           2            4           1 versicolor
#> 74             6           2            4           1 versicolor
#> 75             6           2            4           1 versicolor
#> 76             6           3            4           1 versicolor
#> 77             6           2            4           1 versicolor
#> 78             6           3            5           1 versicolor
#> 79             6           2            4           1 versicolor
#> 80             5           2            3           1 versicolor
#> 81             5           2            3           1 versicolor
#> 82             5           2            3           1 versicolor
#> 83             5           2            3           1 versicolor
#> 84             6           2            5           1 versicolor
#> 85             5           3            4           1 versicolor
#> 86             6           3            4           1 versicolor
#> 87             6           3            4           1 versicolor
#> 88             6           2            4           1 versicolor
#> 89             5           3            4           1 versicolor
#> 90             5           2            4           1 versicolor
#> 91             5           2            4           1 versicolor
#> 92             6           3            4           1 versicolor
#> 93             5           2            4           1 versicolor
#> 94             5           2            3           1 versicolor
#> 95             5           2            4           1 versicolor
#> 96             5           3            4           1 versicolor
#> 97             5           2            4           1 versicolor
#> 98             6           2            4           1 versicolor
#> 99             5           2            3           1 versicolor
#> 100            5           2            4           1 versicolor
#> 101            6           3            6           2  virginica
#> 102            5           2            5           1  virginica
#> 103            7           3            5           2  virginica
#> 104            6           2            5           1  virginica
#> 105            6           3            5           2  virginica
#> 106            7           3            6           2  virginica
#> 107            4           2            4           1  virginica
#> 108            7           2            6           1  virginica
#> 109            6           2            5           1  virginica
#> 110            7           3            6           2  virginica
#> 111            6           3            5           2  virginica
#> 112            6           2            5           1  virginica
#> 113            6           3            5           2  virginica
#> 114            5           2            5           2  virginica
#> 115            5           2            5           2  virginica
#> 116            6           3            5           2  virginica
#> 117            6           3            5           1  virginica
#> 118            7           3            6           2  virginica
#> 119            7           2            6           2  virginica
#> 120            6           2            5           1  virginica
#> 121            6           3            5           2  virginica
#> 122            5           2            4           2  virginica
#> 123            7           2            6           2  virginica
#> 124            6           2            4           1  virginica
#> 125            6           3            5           2  virginica
#> 126            7           3            6           1  virginica
#> 127            6           2            4           1  virginica
#> 128            6           3            4           1  virginica
#> 129            6           2            5           2  virginica
#> 130            7           3            5           1  virginica
#> 131            7           2            6           1  virginica
#> 132            7           3            6           2  virginica
#> 133            6           2            5           2  virginica
#> 134            6           2            5           1  virginica
#> 135            6           2            5           1  virginica
#> 136            7           3            6           2  virginica
#> 137            6           3            5           2  virginica
#> 138            6           3            5           1  virginica
#> 139            6           3            4           1  virginica
#> 140            6           3            5           2  virginica
#> 141            6           3            5           2  virginica
#> 142            6           3            5           2  virginica
#> 143            5           2            5           1  virginica
#> 144            6           3            5           2  virginica
#> 145            6           3            5           2  virginica
#> 146            6           3            5           2  virginica
#> 147            6           2            5           1  virginica
#> 148            6           3            5           2  virginica
#> 149            6           3            5           2  virginica
#> 150            5           3            5           1  virginica