Split delimited strings in a column and insert as new rows [duplicate]

Answer 1

Here's a data.table solution:

d.df <- read.table(header=T, text="V1 | V2
1 | a,b,c
2 | a,c
3 | b,d
4 | e,f", stringsAsFactors=F, sep="|", strip.white = TRUE)
require(data.table)
d.dt <- data.table(d.df, key="V1")
out <- d.dt[, list(V2 = unlist(strsplit(V2, ","))), by=V1]

#    V1 V2
# 1:  1  a
# 2:  1  b
# 3:  1  c
# 4:  2  a
# 5:  2  c
# 6:  3  b
# 7:  3  d
# 8:  4  e
# 9:  4  f

> sapply(out$V2, nchar) # (or simply nchar(out$V2))
# a b c a c b d e f 
# 1 1 1 1 1 1 1 1 1