Iterating over the rows of a data.frame with purrr — Part 2
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A year ago I already wrote an article how to iterate over the rows of a data.frame.
Now I’ve run into another special case. Last year we used pmap_dfr() to pass
each element of a row as single parameter to our custom function.
But what should you do if your function accepts a data.frame (or list) as one single parameter?
The function …
But let’s look at our example first:
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my_function <- function(repeated = 1, text = "a", number_rows = 2) {
row <- data.frame(
`repeated` = repeated,
`text` = text,
`number_rows` = number_rows,
generated_text = paste(replicate(repeated, text), collapse = "")
)
return(do.call("rbind", replicate(number_rows, row, simplify = FALSE)))
}
my_function(3, "Hello ", 4)
|
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## repeated text number_rows generated_text ## 1 3 Hello 4 Hello Hello Hello ## 2 3 Hello 4 Hello Hello Hello ## 3 3 Hello 4 Hello Hello Hello ## 4 3 Hello 4 Hello Hello Hello |
Let’s change this function a little bit:
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my_new_function <- function(input_data) {
row <- data.frame(
`repeated` = input_data$repeated,
`text` = input_data$text,
`number_rows` = input_data$number_rows,
generated_text = paste(replicate(input_data$repeated, input_data$text), collapse = "")
)
return(do.call("rbind", replicate(input_data$number_rows, row, simplify = FALSE)))
}
input_data <- data.frame(
repeated = 3,
text = "Hello ",
number_rows = 4
)
my_new_function(input_data)
|
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## repeated text number_rows generated_text ## 1 3 Hello 4 Hello Hello Hello ## 2 3 Hello 4 Hello Hello Hello ## 3 3 Hello 4 Hello Hello Hello ## 4 3 Hello 4 Hello Hello Hello |
… and its parameters
Now we want to call the function my_new_function with each row of the
following data.frame as parameter:
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options(tidyverse.quiet = TRUE) library(tidyverse, warn.conflicts = FALSE) parameters <- tribble( ~repeated, ~text, ~number_rows, 1, "one", 3, 2, "two", 2, 3, "three", 1 ) %>% as.data.frame() parameters |
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## repeated text number_rows ## 1 1 one 3 ## 2 2 two 2 ## 3 3 three 1 |
Iterating again
Using purrr::pmap_dfr() won’t work because our function expects one single
argument.
So we use purrr::pmap() to convert each row into a data.frame and combine
these data.frames to a list. Then we can use purrr::map_dfr().
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parameters %>% purrr::pmap(data.frame) %>% purrr::map_dfr(my_new_function) |
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## repeated text number_rows generated_text ## 1 1 one 3 one ## 2 1 one 3 one ## 3 1 one 3 one ## 4 2 two 2 twotwo ## 5 2 two 2 twotwo ## 6 3 three 1 threethreethree |
Notes
When I had found the above solution for my problem I googled for a solution
with one single purrr function call. During this search I found this
page
by Jenny Bryan who is very inspiring for all
purrr related stuff.
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