[R] factor as seq() in for loop

[Gabor Grothendieck]

On 9/19/05, Tord Snall <Tord.Snall at helsinki.fi> wrote:
> Dear all,
> I would like to use the values in vegaggr.BLMCMR02$colony
> 
> str(vegaggr.BLMCMR02)
> `data.frame':   1678 obs. of  3 variables:
> $ vegtype       : Factor w/ 27 levels "2010","2020",..: 3 4 5 19 4 5 19 5
> $ colony        : Factor w/ 406 levels "0","1","10","100",..: 1 1 1 1 2 2 2
> $ Totvegproparea: num  0.00055 0.03956 0.95705 0.00284 0.05215 ...
> 
> as the seq in a for loop (for(var in seq)), and therefore first picked them
> out as
> cols = aggregate(list(A = vegaggr.BLMCMR02$Totvegproparea),
>                list(colony = vegaggr.BLMCMR02$colony), sum)[,1]
> > str(cols)
>  Factor w/ 406 levels "0","1","10","100",..: 1 2 3 4 5 6 7 8 9 10 ...
> 
> I next planned to transform cols using as.integer(cols). However, this
> transformation gives a vector corresponding to seq(from=1,to=length(cols)).
> 
> Could someone please give advice on how to make use of a factor as the seq
> in a for loop (which is strictly not allowed' according to ?Control).
> 

What are you trying to loop over?

Species <- head(iris$Species)
for(i in seq(Species)) print(Species[i])

will loop over the elements of the factor Species and you can use

for(lev in levels(Species)) print(lev)

to loop over its levels.