how to apply same function to multiple dataframes in R - r

Question

I am applying the same function to multiple dataframes. For example, I want to merge the column2 and column3 in df1. After applying this function, the df1 will get a new column called col2_col3.
df1 <- data.frame(x = rep(3, 5), y = seq(1, 5, 1), ID = letters[1:5])
df2 <- data.frame(x = rep(5, 5), y = seq(2, 6, 1), ID = letters[6:10])
#I define a function:
PasteTwoColumn <- function(x)
{
x$col2_col3 <- paste(x[,2], x[,3], sep = "_")
return(x)
}
#apply the function to the df1, it works.
df1 <- PasteTwoColumn(df1)
# but I failed by an lappy function, because it returns a list, not the dataframe
mylist <- list(df1, df2)
result <- lapply(mylist, PasteTwoColumn)
I want to continue to apply this function to all my dataframes, eg. df1, df2, df3 ...df100. The output file should keep the same type of dataframe and the name. The lapply function does not work, because it returns a list, not the separate data frame.

Answer 1

We can keep the datasets in a list and loop over the list with lapply
lst1 <- lapply(list(df1, df2), PasteTwoColumn)
If there are many datasets, use mget to get the values of the datasets into a list
lst1 <- lapply(mget(paste0('df', 1:100)), PasteTwoColumn)
Or instead of paste, we can also use ls
lst1 <- lapply(mget(ls(pattern = '^df\\d+$')), PasteTwoColumn)
If we need to update the original object, use list2env
list2env(lst1, .GlobalEnv) #not recommended though
If we need to use a for loop
for(obj in paste0("df", 1:100)) {
assign(obj, PasteTwoColumn(get(obj)))
}