Text file to list in R - list

Question

I have a large text file with a variable number of fields in each row. The first entry in each row corresponds to a biological pathway, and each subsequent entry corresponds to a gene in that pathway. The first few lines might look like this
path1 gene1 gene2
path2 gene3 gene4 gene5 gene6
path3 gene7 gene8 gene9
I need to read this file into R as a list, with each element being a character vector, and the name of each element in the list being the first element on the line, for example:
> pathways <- list(
+ path1=c("gene1","gene2"),
+ path2=c("gene3","gene4","gene5","gene6"),
+ path3=c("gene7","gene8","gene9")
+ )
>
> str(pathways)
List of 3
$ path1: chr [1:2] "gene1" "gene2"
$ path2: chr [1:4] "gene3" "gene4" "gene5" "gene6"
$ path3: chr [1:3] "gene7" "gene8" "gene9"
>
> str(pathways$path1)
chr [1:2] "gene1" "gene2"
>
> print(pathways)
$path1
[1] "gene1" "gene2"
$path2
[1] "gene3" "gene4" "gene5" "gene6"
$path3
[1] "gene7" "gene8" "gene9"
...but I need to do this automatically for thousands of lines. I saw a similar question posted here previously, but I couldn't figure out how to do this from that thread.
Thanks in advance.

Answer 1

Here's one way to do it:
# Read in the data
x <- scan("data.txt", what="", sep="\n")
# Separate elements by one or more whitepace
y <- strsplit(x, "[[:space:]]+")
# Extract the first vector element and set it as the list element name
names(y) <- sapply(y, `[[`, 1)
#names(y) <- sapply(y, function(x) x[[1]]) # same as above
# Remove the first vector element from each list element
y <- lapply(y, `[`, -1)
#y <- lapply(y, function(x) x[-1]) # same as above

Answer 2

One solution is to read the data in via read.table(), but use the fill = TRUE argument to pad the rows with fewer "entries", convert the resulting data frame to a list and then clean up the "empty" elements.
First, read your snippet of data in:
con <- textConnection("path1 gene1 gene2
path2 gene3 gene4 gene5 gene6
path3 gene7 gene8 gene9
")
dat <- read.table(con, fill = TRUE, stringsAsFactors = FALSE)
close(con)
Next we drop the first column, first saving it for the names of the list later
nams <- dat[, 1]
dat <- dat[, -1]
Convert the data frame to a list. Here I just split the data frame on the indices 1,2,...,n where n is the number of rows:
ldat <- split(dat, seq_len(nrow(dat)))
Clean up the empty cells:
ldat <- lapply(ldat, function(x) x[x != ""])
Finally, apply the names
names(ldat) <- nams
Giving:
> ldat
$path1
[1] "gene1" "gene2"
$path2
[1] "gene3" "gene4" "gene5" "gene6"
$path3
[1] "gene7" "gene8" "gene9"

Answer 3

A quick solution based on the linked page...
inlist <- strsplit(readLines("file.txt"), "[[:space:]]+")
pathways <- lapply(inlist, tail, n = -1)
names(pathways) <- lapply(inlist, head, n = 1)

Answer 4

One more solution:
sl <- c("path1 gene1 gene2", "path2 gene1 gene2 gene3") # created by readLines
f <- function(l, s) {
v <- strsplit(s, " ")[[1]]
l[[v[1]]] <- v[2:length(v)]
return(l)
}
res <- Reduce(f, sl, list())