Aggregate multiple rows of the same data.frame in R based on common values in given columns

Question

I have a data.frame that looks like this:

# set example data
df <- read.table(textConnection(\"item\\tsize\         


        

Answer 1

Nowadays, this is what I would do:

library(dplyr)

df %>%
  group_by(item, size, weight) %>%
  summarize(value = mean(value)) %>%
  ungroup

This yields the following result:

# A tibble: 3 x 4
   item  size weight value
      
1     A     2      3     5
2     B     1      2     3
3     C     3      2     1

I will leave the accepted answer as such as I specifically asked for aggregate, but I find the dplyr solution the most readable.