list variables by group as character string in data frame column

Question

I have a data set with the following structure:

df1 <- data.frame(
session = seq(1,10,1))

df2 <- data.frame(
session = rep(1:10, each=4),
sample = seq(1,40,1))

What I need returned is a df1 with the following structure:

session | sample.list
 1      |    1,2,3,4
 2      |    5,6,7,8
 3      |    9,10,11,12
...

Basically its lists all the samples taken within a given session.

Thanks for any pointers or solutions to solve this.

akrun · Accepted Answer · 2015-02-10T11:05:59.780

2

With base R

aggregate(sample ~ session, df2, toString)

Or (depends on the type of the desired result)

aggregate(sample ~ session, df2, list)

Or using data.table

library(data.table)
setDT(df2)[, list(sample.list=toString(sample)), session]

Or if you need the column as list

setDT(df2)[, list(sample.list=list(sample)), session]

For listing unique "samples"

 aggregate(sample ~ session, df2, function(x) toString(unique(x)))

Or

 setDT(df2)[, list(toString(unique(sample))), session]

edited Feb 10 '15 at 11:05

answered Feb 10 '15 at 10:33

akrun

Concise and best solution! – Colonel Beauvel Feb 10 '15 at 10:37
@ColonelBeauvel Thanks, but your solution can be made concise using `ddply` or dplyr – akrun Feb 10 '15 at 10:38
I let you adding the plyr solution! – Colonel Beauvel Feb 10 '15 at 10:38
@ColonelBeauvel I am not adding it, you can modify your solution. – akrun Feb 10 '15 at 10:39
one extension to the original question - is there a way to just list unique samples in the column sample.list? I have some sessions where the same samples were repeated. – doncarlos Feb 10 '15 at 10:47

1 Answers1