在 R 中使用 tapply(dataframe, index, function) 作为 function 2 列的参数

Question

I would like to use the tapply() function on a dataframe, grouping the rows with the indexing. My problem is that the argument I would pass to the function is not a single column, but a pair of columns. This beacause the 2 columns of the data frame represent xy points, which are intended as couples. Running tapply(dataframe, indexes, function) gives me the error that indexes has length different from tapply. How can I solve this? Thank you!

Answer 1

If there are more than one column to be summarised, use aggregate instead of tapply (as tapply works for a single column)

aggregate(.~ indexes, transform(df1, indexes = indexes), FUN = yourfun)

---

Or another option is by

by(df1, list(indexes), FUN = yourfun)

---

Or it may be more flexible with tidyverse

library(dplyr)
df1 %>%
    group_by(indexes) %>%
    summarise(across(c(x, y), yourfun), .groups = 'drop')

---

Using a small reproducible example

indexes = rep(1:2, c(3, 2))
by(mtcars[1:5, 1:5], indexes, FUN = sum)