R collapse multiple rows into 1 row - same columns

Question

This is piggy backing on a question I answered last night as I am reconsidering how I\'d like to format my data. I did search but couldn\'t find up with any applicable answe

Answer 1

As you suggested that you would like a data.table solution in your comment, you could use

library(data.table)
df <- data.table(record_numb,col_a,col_b,col_c)

df[, lapply(.SD, paste0, collapse=""), by=record_numb]
   record_numb col_a col_b col_c
1:           1   123   234   543
2:           2   987   765   543

.SD basically says, "take all the variables in my data.table" except those in the by argument. In @Frank's answer, he reduces the set of the variables using .SDcols. If you want to cast the variables into numeric, you can still do this in one line. Here is a chaining method.

df[, lapply(.SD, paste0, collapse=""), by=record_numb][, lapply(.SD, as.integer)]

The second "chain" casts all the variables as integers.