Question

Using R, if I have a 2 column data frame:

meta <- c(1,2,2,3,4,4,4,5)
value <- c("a","b","c","d","e","f","g","h")
df <- data.frame(meta,value)
df
  meta value
1    1     a
2    2     b
3    2     c
4    3     d
5    4     e
6    4     f
7    4     g
8    5     h

How would I go about combining “value” with a delimiter (like ||) by repeated “meta” such that the resulting data frame would look like:

  meta   value
1    1       a
2    2    b||c
3    3       d
4    4 e||f||g
5    5       h

Thanks!

Answer 1

Using the plyr package the following works

library(plyr)
> ldply(split(df,meta),function(x){paste(x$value,collapse="||")})
  .id      V1
1   1       a
2   2    b||c
3   3       d
4   4 e||f||g
5   5       h

or

> ddply(df,.(meta),function(x){c(value=paste(x$value,collapse="||"))})
  meta   value
1    1       a
2    2    b||c
3    3       d
4    4 e||f||g
5    5       h

if you want to preserve names