[R] how to use by() ?

[Greg Johnson]

Jim Moon <moonja <at> ohsu.edu> writes:

> How might one accomplish this using the by() function?
> m1 is a data frame.
> 
> # populate column "m1$major_allele"
> for ( i in 1:length(m1$major_allele)) {
>   if ( m1$Freq1[i] == m1$MAF[i]){
>     m1$major_allele[i] = m1$Al1[i]
>   }
>   else{
>      m1$major_allele[i] = m1$Al2[i]
>   }
> }

You could use:

m1$major_allele <- ifelse(  m1$Freq1 == m1$MAF, m1$Al1,  m1$Al2 )

Greg