Collapse text by group in data frame

Question

How do I aggregate data frame by group in column group and collapse text in column text?

Sample data:

df <- read.table(header=T, text="
group text
a a1
a a2
a a3
b b1
b b2
c c1
c c2
c c3
")

Required output (data frame):

group text
a     a1a2a3
b     b1b2
c     c1c2c3

Now I have:

sapply(unique(df$group), function(x) {
  paste0(df[df$group==x,"text"], collapse='')
})

This works to some extent as it returns text properly collapsed by group, but as a vector:

[1] "a1a2a3" "b1b2"   "c1c2c3"

I need a data frame with group column as a result.

Answer 1

Simply use aggregate :

aggregate(df$text, list(df$group), paste, collapse="")
##   Group.1      x
## 1       a a1a2a3
## 2       b   b1b2
## 3       c c1c2c3

Or with plyr

library(plyr)
ddply(df, .(group), summarize, text=paste(text, collapse=""))
##   group   text
## 1     a a1a2a3
## 2     b   b1b2
## 3     c c1c2c3

ddply is faster than aggregate if you have a large dataset.

EDIT : With the suggestion from @SeDur :

aggregate(text ~ group, data = df, FUN = paste, collapse = "")
##   group   text
## 1     a a1a2a3
## 2     b   b1b2
## 3     c c1c2c3

For the same result with earlier method you have to do :

aggregate(x=list(text=df$text), by=list(group=df$group), paste, collapse="")

EDIT2 : With data.table :

library("data.table")
dt <- as.data.table(df)
dt[, list(text = paste(text, collapse="")), by = group]
##    group   text
## 1:     a a1a2a3
## 2:     b   b1b2
## 3:     c c1c2c3

Answer 2

You can use dplyr package for this

library(dplyr)

df %>%
  group_by(group) %>%
  summarise(text=paste(text,collapse=''))