Lookup value from another column that matches with variable

Question

I have a dataframe that looks like:

animal_id   trait_id    sire_id dam_id
    1         25.05        0       0
    2         -46.3        1       2
    3                


        

Answer 1

You can do this using match (in base R) in one run (no need to loop over)

df[c("trait_sire", "trait_dam")] <- 
cbind(with(df, trait_id[match(sire_id, animal_id)]), 
      with(df, trait_id[match(dam_id, animal_id)]))

  # animal_id trait_id sire_id dam_id trait_sire trait_dam
# 1         1    25.05       0      0         NA        NA
# 2         2   -46.30       1      2      25.05    -46.30
# 3         3    41.60       1      2      25.05    -46.30
# 4         4   -42.76       3      4      41.60    -42.76
# 5         5   -10.99       3      4      41.60    -42.76
# 6         6   -49.81       5      4     -10.99    -42.76