# Re: [R] by() subset by factor gives unexpected results

```The answer was (thanks to Mark Leeds) to do with the use of a factor
```
on [2017-08-05] at 08:57 Myles English writes:

> I am having trouble understanding how the 'by' function works.  Using
> this bit of code:
>
> i <- data.frame(x=c(1,2,3), y=c(0,0,0), B=c("red","blue","blue"))
> j <- data.frame(x=c(1,2,3), y=c(1,1,1), B=c('red','blue','green'))

The use of I() prevents conversion to a factor:

i <- data.frame(x=c(1,2,3), y=c(0,0,0), B=I(c("red","blue","blue")))
j <- data.frame(x=c(1,2,3), y=c(1,1,1), B=I(c('red','blue','green')))

> plot(0, 0, type="n", xlim=c(0,4), ylim=c(0,1))
> by(i, i\$B, function(s){ points(s\$x, s\$y, col=s\$B) })
> by(j, j\$B, function(s){ points(s\$x, s\$y, col=s\$B) })
>
> I would have expected the point at (1,1) to be coloured red.  When
> plotted, this row is indeed red:
>
>> i[1,]
>   x y   B
> 1 1 0 red
>
> however, this next point is green on the plot even though I would like
> it to be red:
>
>> j[1,]
>   x y   B
> 1 1 1 red
>
> How can I achieve that?
>
> Myles

______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help