Read from a list of csv filenames into R

Question

I am looking into importing multiple csv files in R

temp = list.files(pattern="*.csv")
for (i in 1:length(temp)) assign(temp[i], read.csv(temp[i]))

however

temp[1] returns "something.csv"
.......

is there something wrong with my code?

Answer 1

SOLUTION:

Fixes: 1) must use double-[[]] to get the individual list element 2) don't use assign()

So either:

for (i in 1:length(temp)) { temp[[i]] <- read.csv(temp[i]) }

or, if you don't want to overwrite the temp variable:

df = c(rep(data.frame(), length(temp))) # list of empty dataframe
for (i in 1:length(temp)) { df[[i]] <- as.list(read.csv(temp[i])) }

There were two separate mistakes in your original code:

1. using single [] instead of double [[]]. Single [] gives you a list slice containing one element (not what you want to assign to), instead of just that actual element.

2. assign is not doing what you think it's doing, as @G-Grothendieck said.

You simply want to do temp[[i]] <- read.csv(temp[i])

But what you're actually doing is assigning to the variable whose name is contained in temp[i]. So if temp[i] is 'whosyour.csv', you're actually creating and assigning to a variable with that name, rather than assigning to temp[i] itself:

whosyour.csv <- read.csv('whosyour.csv') # NOT WHAT YOU WANTED!

Answer 2

No need for for looping in R when we have sapply (and the other *apply functions).

In this case, with no further arguments sapply returns a named list of data frames, which I will call read.all.

> temp <- list.files(pattern = "*.csv")
> read.all <- sapply(temp, read.csv)

Looking at read.all shows that it is a named list of data frames.

You can then access the individual data frames by file name with

> read.all[["filename.csv"]]  ## or read.all["filename.csv"]

or with the $ operator

> read.all$filename.csv

Answer 3

Try this:

temp <- list.files(pattern = "*.csv")
## for individual files
dataset <- lapply(temp,FUN=function(files){read.table(files,header=TRUE, sep=",")})
dataset[1] ## for specific files of interest, OR
## If your CSV column structure is same across all csv's bind them all into 1 file
dataset <- do.call("rbind",lapply(temp,FUN=function(files){read.table(files,header=TRUE, sep=",")}))