strsplit and lapply

Question

I have a string in some text of the form "12,34,77", including the quotation marks.

I need to get the values of each of those numbers into a list. I tried using lapply and strsplit:

control2=lapply(strsplit(data$values,","),as.numeric)

but I get the error:

non character argument

What am I doing wrong?

Answer 1

1) strapply

1a) scalar Here is a one-liner using strapply from the gsubfn package:

library(gsubfn)
x <- '"12,34,567"'

strapply(x, "\\d+", as.numeric, simplify = c)
## [1]  12  34 567

1b) vectorized A vectorized version is even simpler -- just remove the simplify=c like this:

v <- c('"1,2,3"', '"8,9"') # test data
strapply(v, "\\d+", as.numeric)`

2) gsub and scan

2a) scalar and here is a one-linear using gsub and scan:

scan(text = gsub('"', '', x), what = 0, sep = ",")
## Read 3 items
## [1]  12  34 567

2b) vectorized A vectorized version would involve lapply-ing over the components:

lapply(v, function(x) scan(text = gsub('"', '', x), what = 0, sep = ","))

3) strsplit

3a) scalar and here is a strsplit solution. Note that we split on both " and , :

as.numeric(strsplit(x, '[",]')[[1]][-1])
## [1]  12  34 567

3b) vectorized A vectorized solution would, again, involve lapply-ing over the components:

lapply(v, function(x) as.numeric(strsplit(x, '[",]')[[1]][-1]))

3c) vectorized - simpler or slightly simpler:

lapply(strsplit(gsub('"', '', v), split = ","), as.numeric)

Answer 2

I think your problem may stem from your source data. In any case, if you want to work with numbers, you will have get rid of quotes. I recommend gsub.

> x <- '"1,3,5"'
> x
[1] "\"1,3,5\""
> x <- gsub("\"", "", x)
> x
[1] "1,3,5"
> as.numeric(unlist(strsplit(x, ",")))
[1] 1 3 5

Answer 3

Try this:

x <-  "12,34,77"
sapply(strsplit(x, ",")[[1]], as.numeric, USE.NAMES=FALSE)
[1] 12 34 77

Since the result of strsplit() is a list of lists, you need to extract the first element and pass this to lapply().

---

If, however, your string really containst embedded quotes, you need to remove the embedded quotes first. You can use gsub() for this:

x <-  '"12,34,77"'
sapply(strsplit(gsub('"', '', x), ",")[[1]], as.numeric, USE.NAMES=FALSE)
[1] 12 34 77

Answer 4

As has already been pointed out, you need to regex out the quotation marks first.

The destring function in the taRifx library will do that (remove any non-numeric characters) and then coerce to numeric:

test <- '"12,34,77"'
library(taRifx)
lapply(strsplit(test,","),destring)
[[1]]
[1] 12 34 77