splitting text in column and add row number [duplicate]

Question

This question already has an answer here:

• Split comma-separated strings in a column into separate rows 5 answers

I would like to split some text in a data frame column and save it into a data frame together with the row number or an id column.

I normally used plyr to do that, but this is no longer working in dplyr.

If I understand it correctly, it is more a bug in plyr and my code works since it is a bug.

So I am looking for the correct way to do this.

This is a minimal example in plyr:

library(plyr)
set.seed(1)
df <- data.frame(a=seq(2), 
                 b=c(paste(sample(letters,3), collapse=';'),
                     paste(sample(letters,3), collapse=';')),               
                 stringsAsFactors=FALSE)
ddply(df,.(a),summarise,unlist(strsplit(b,';')))

It turns the original data frame:

  a     b
1 1 g;j;n
2 2 x;f;v

Into this:

  a ..1
1 1   g
2 1   j
3 1   n
4 2   x
5 2   f
6 2   v

What would be the correct dplyr solution?

Answer 1

I'm biased in favor of cSplit from the "splitstackshape" package, but you might be interested in unnest from "tidyr" in conjunction with "dplyr":

library(dplyr)
library(tidyr)
df %>%
  mutate(b = strsplit(b, ";")) %>%
  unnest(b)
#   a b
# 1 1 g
# 2 1 j
# 3 1 n
# 4 2 x
# 5 2 f
# 6 2 v

Answer 2

You could do this using cSplit from splitstackshape

library(splitstackshape)
cSplit(df, 'b', ';', 'long')
#   a b
#1: 1 g
#2: 1 j
#3: 1 n
#4: 2 x
#5: 2 f
#6: 2 v

Or using dplyr/tidyr

library(dplyr)
library(tidyr)
separate(df, b, c('b1', 'b2', 'b3'), sep=";") %>%
                               gather(Var, b, -a) %>% 
                               select(-Var) %>% 
                               arrange(a)

Or another option would be to use do

df %>%
   group_by(a) %>% 
   do(data.frame(b=unlist(strsplit(.$b, ';'))))