Passing a function to multiple dataframes at the same time

Question

I have 3 dataframes:

iris1<-iris[1:50, ]
iris2<-iris[51:100,]
iris3<-iris[101:150,]

And a simple function that takes the input of a dataframe and a column and multiplies that column by 100 and then returns the dataframe:

add_col<-function(df,colname)
{
df$newcol<-df [, colname]*100
return(df) 
}

I can then use that function on a dataframe to get the extra column added:

iris1<-add_col(df=iris1,colname="Sepal.Length")

How can I pass all the dataframes to this function rather than repeating the above 3x (1 for each dataframe?). I assume this is a problem that will use the apply family for functions but I can't work out how to do it.

deschen · Accepted Answer · 2022-02-27 14:21:36Z

3

You can do:

new_list <- lapply(list(iris1, iris2, iris3), add_col, colname = "Sepal.Length")

Here, you will have the three data frames as list elements and you could get them back as real data frames by e.g.:

iris1_new <- new_list[[1]]

Or you can do the following to assign the new list elements to the global environment:

new_names <- c("iris1_new", "iris2_new", "iris3_new")
lapply(1:length(new_names), function(x) assign(x = new_names[x], value = new_list[[x]], envir = .GlobalEnv))

edited Feb 27, 2022 at 14:21

answered Feb 27, 2022 at 14:16

deschen

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PaulS · Accepted Answer · 2022-02-28 13:06:14Z

1

Another possible solution, based on purrr::map:

library(tidyverse)

x <- c("iris1", "iris2", "iris3")

map(map(x, ~ as.symbol(.x) %>% eval),
    ~ add_col(.x, "Sepal.Length")) %>%
  set_names(x) %>%
  list2env(.GlobalEnv)

edited Feb 28, 2022 at 13:06

answered Feb 27, 2022 at 16:41

PaulS

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2 Comments

Basil Over a year ago

is there a way to just pass a vector into this code rather than having to type out iris1, iris2, iris3 twice (once for the map function and then once for set_names)? For example to have code earlier on to designate the df's as iris_dfs<-c("iris1","iris2","iris3")

PaulS Over a year ago

Yes, @Basil, see my edited solution.

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