How would you loop this in R?

Question

I have this kinda simple task I'm having hard time looping.

So, lets assume I have this tibble:

library(tidyverse)
dat <- tibble(player1 = c("aa","bb","cc"), player2 = c("cc","aa","bb"))

My goal here, is to make three new columns ( for each unique "player" I have) and assign value of 1 to the column, if the player is "player1", -1 if the player is "player2" and 0 otherwise.

Previously, I have been doing it like this:

dat %>% mutate( aa = ifelse(player1 == "aa",1,ifelse(player2 == "aa",-1,0)),
          bb = ifelse(player1 == "bb",1,ifelse(player2 == "bb",-1,0)),
          cc = ifelse(player1 == "cc",1,ifelse(player2 == "cc",-1,0)))

This works, but now I have hundreds of different "players", so it would seem silly to do this manually like that. I have tried and read about loops in R, but I just can't get this one right.

Answer 1

Using model.matrix() from base R:

dat[unique(dat$player1)] <- 
  model.matrix(~0+ player1, data = dat) - model.matrix(~0+ player2, data = dat)

dat
  player1 player2    aa    bb    cc
  <chr>   <chr>   <dbl> <dbl> <dbl>
1 aa      cc          1     0    -1
2 bb      aa         -1     1     0
3 cc      bb          0    -1     1

This assumes you have all players in both columns. Otherwise you would need to convert them to factors with the appropriate levels and replace unique with levels.