R: split string into numeric and return the mean as a new column in a data frame

Question

I have a large data frame with columns that are a character string of numbers such as \"1, 2, 3, 4\". I wish to add a new column that is the average of these numbers. I have

Answer 1

library(data.table)
cols <- paste0("a",1:4)
setDT(df)[, (cols) := tstrsplit(a, ",", fixed=TRUE, type.convert=TRUE)
        ][, .(Mean = rowMeans(.SD)), .SDcols = cols]
   Mean
1:  2.5
2:  5.0
3:  7.5

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Alternatively,

rowMeans(setDT(tstrsplit(df$a, ",", fixed=TRUE, type.convert=TRUE)))
# [1] 2.5 5.0 7.5