I have a number of dataframes (imported from CSV) that have the same structure. I would like to loop through all these dataframes and keep only two of these columns.
The loop below does not seem to work, any ideas why? Would ideally like to do this using a loop as I am trying to get better at using these.
frames <- ls()
for (frame in frames){
frame <- subset(frame, select = c("Col_A","Col_B"))
}
Cheers in advance for any advice.
For anyone interested I used Richard Scriven's idea of reading in the dataframes as one object, with a function added that showed where the file had been imported from. This allowed me to then use the Plyr package to manipulate the data:
library(plyr)
dataframes <- list.files(path = TEESMDIR, full.names = TRUE)
## Define a function to add the filename to the dataframe
read_csv_filename <- function(filename){
ret <- read.csv(filename)
ret$Source <- filename #EDIT
ret
}
list_dataframes <- ldply(dataframes, read_csv_filename)
selection <- llply(list_dataframes, subset, select = c(var1,var3))
The basic problem is that ls() returns a character vector of all the names of the objects in your environment, not the objects themselves. To get and replace an object using a character variable containing it's name, you can use the get()/assign() functions. You could re-write your function as
frames <- ls()
for (frame in frames){
assign(frame, subset(get(frame), select = c("Col_A","Col_B")))
}
assign can be dangerous as well.
list, notls; 2) you need to supply the indices to frame, as inframes[[frame]] <- subset(...); 3) "frame in frames" doesn't make sense since you just created a null list withframes <- list()-- it should be likefor (frame in 1:5)ls, which I would not recommendcolClassesto only read the columns you want. Details here.rm(list = ls())followed byframes <- lapply(files, read.table), wherefilesis a vector of file names