Flatten list column in data frame with ID column

Question

My data frame contains the output of a survey with a select multiple question type. Some cells have multiple values.

df <- data.frame(a=1:3,b=I(list(1,1:2         


        

Answer 1

Here's one way, with data.table:

require(data.table)
data.table(df)[,as.integer(unlist(b)),by=a]

If b is stored consistently, as.integer can be skipped. You can check with

unique(sapply(df$b,class))
# [1] "numeric" "integer"