In R, how can I collapse a string variable in a data frame, by a grouping variable? In other words, pasting vertically instead of horizontally

Question

I have the following example data frame:

model <- c(1,1,1,1,2,2,3,3,3)

variable <- letters[seq(1:9)]

df <- data.frame(model , variable)

  model variable
1     1        a
2     1        b
3     1        c
4     1        d
5     2        e
6     2        f
7     3        g
8     3        h
9     3        i

and I would like to "collapse" the field variable grouped by model. If variable were numeric it would be a sum, or some other operator. However, this being character, I would like to paste the values.

  model variable
1     1  a b c d
2     2      e f
3     3    g h i

If you wish to collapse several different columns, see [**here**](http://stackoverflow.com/questions/26981385/r-collapse-all-columns-by-an-id-column/26981611#26981611) — Henrik, Dec 03 '14 at 13:53

score 2 · Answer 1 · answered Dec 03 '14 at 13:48

2

You can use aggregate:

aggregate(variable ~ model, df, paste, collapse = " ")
#   model variable
# 1     1  a b c d
# 2     2      e f
# 3     3    g h i

answered Dec 03 '14 at 13:48

Sven Hohenstein

78,180
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Thank you!!! Any chance on collapsing multiple character fields in the same aggregate function? if not, this is awesome enough! – Illya-Big Dec 03 '14 at 14:34
@Illya-Big What is the expected output in this case? – Sven Hohenstein Dec 03 '14 at 14:35
@Illya-Big Did you even bother to check the link in my comment? – Henrik Dec 03 '14 at 14:49

score 2 · Answer 2 · answered Dec 03 '14 at 13:52

2

...or dcast from the reshape2 package:

> reshape2::dcast(df, model~., value.var = "variable", fun.aggregate = paste,
                  collapse = " ")
  model       .
1     1 a b c d
2     2     e f
3     3   g h i

answered Dec 03 '14 at 13:52

krlmlr

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score 1 · Answer 3 · answered Dec 03 '14 at 13:56

1

Or using data.table

 library(data.table)
 setDT(df)[,  list(variable=paste(variable, collapse=' ')), by=model]
 #   model variable
 #1:     1  a b c d
 #2:     2      e f
 #3:     3    g h i

answered Dec 03 '14 at 13:56

akrun

789,025
32
460
575

Thank you. This is also great. – Illya-Big Dec 03 '14 at 14:35

In R, how can I collapse a string variable in a data frame, by a grouping variable? In other words, pasting vertically instead of horizontally

3 Answers3