Calculate group mean, sum, or other summary stats. and assign column to original data

Solution 1:

You may do this in dplyr using mutate:

library(dplyr)
df %>%
  group_by(group) %>%
  mutate(grp.mean.values = mean(value))

...or use data.table to assign the new column by reference (:=):

library(data.table)
setDT(df)[ , grp.mean.values := mean(value), by = group]

Have a look at the ave function. Something like

df$grp.mean.values <- ave(df$value, df$group)

If you want to use ave to calculate something else per group, you need to specify FUN = your-desired-function, e.g. FUN = min:

df$grp.min <- ave(df$value, df$group, FUN = min)