How to conditionally remove quotes in write.csv?

Question

When using write.csv, one may reduce file sizes significantly (approx 25% for large datasets) by removing quotes using quote=FALSE. However, this may cause read.csv to malfunction if commas are present in your data. For example:

x <- data.frame(a=1:2,b=c("hello,","world"))
dim(x)
[1] 2 2
f <- tempfile()
write.csv(x,f,row.names=FALSE,quote=FALSE)
dim(read.csv(f))
[1] 2 2
read.csv(f)
      a  b
1 hello NA
2 world NA

Observe column name misalignment and a loss of data and addition of spurious data.

Is is possible to remove quotes generally, but maintain them for fields that have commas in the data?

Answer 1

The solution I went with was a combination of the comments of @TimPietzcker and @BenBolker.

quote can be a numeric vector to specify which columns get quoted. While I would have preferred to only quote when needed, this allowed almost the full file-size reduction in my case (also using na="").

commas <- which(sapply(x, function(y) any(grepl(",",y))))
write.csv(x,f,row.names=FALSE,quote=commas)
read.csv(f)
  a      b
1 1 hello,
2 2  world