Select a numeric columns of a dataframe in a list - r

Question

I have a list of dataframes. After applying a function I get new columns that are non numeric. From each resulting dataframe that I save in a list modified_list As a result I want to save my modified dataframes but I only want to save the columns that contain numeric values.
I am stocked in the selection of numeric columns. I do not know how to select numeric columns on a list of dataframes. My code looks something like this. Please do you have any idea what can i do to make this code work?
library(plyr)
library(VIM)
data1 <- sleep
data2 <- sleep
data3 <- sleep
# get a list of dataframes
list_dataframes <- list(data1, data2, data3) # list of dataframes
n <- length(list_dataframes)
# apply function to the list_dataframes
modified_list <- llply(list_dataframes, myfunction)
# selects only numeric results
nums <- llply(modified_list, is.numeric)
# saving results
for (i in 1:n){
write.table(file = sprintf( "myfile/%s_hd.txt", dataframes[i]), modified_list[[i]][, nums], row.names = F, sep=",")
}

Answer 1

It sounds like you want to subset each data.frame in a list of data.frames to their numeric columns.
You can test which columns of a data.frame called df are numeric with
sapply(df, is.numeric)
This returns a logical vector, which can be used to subset your data.frame like this:
df[sapply(df, is.numeric)]
Returning the numeric columns of that data.frame. To do this over a list of data.frames df_list and return a list of subsetted data.frames:
lapply(df_list, function(df) df[sapply(df, is.numeric)])
Edit: Thanks #Richard Scriven for simplifying suggestion.