group_by function in R

General
#1

Error in group_by function while downloading dplyr package. It doesn't recognize my specific function. Does anyone know the reason?

Thank you

#2

Please post the code you ran and the output that it produced.

#3

Specifically I need to do the sum of 3 columns, grouped by the variable of a fourth column. I need to use group_by and colSums functions. Right?

#4