R: How to remove rows and add the value of a variable to the previous row as a comma separated value? [duplicate]

Answer 1

We can group by 'col1' and paste the 'col2' with collapse=',' option. A convenient wrapper would be toString. This can be done with any of the aggregate by group functions. For example, with data.table, we convert 'data.frame' to 'data.table' (setDT(df1)) and use the logic as described above

library(data.table)
setDT(df1)[, list(col2 = toString(col2)), by = col1]

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Or with aggregate from base R

aggregate(col2~col1, df1, FUN=toString)

If you need a list output for 'col2'

aggregate(col2~col1, df1, FUN=I)

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Or using dplyr

library(dplyr)
df1 %>% 
     group_by(col1) %>% 
     summarise(col2= toString(col2))