# [R] how to get the numbers of factors in a matrix

PIKAL Petr petr.pikal at precheza.cz
Tue Jan 21 11:14:30 CET 2014

```Hi

It is rather difficult to understand what problem you have.

post some data e.g. by

Maybe your problem is in a factor feature that it preserves also empty levels until you specifically drop them.

> ff<-factor(letters[1:5])
> levels(ff[1:2])
[1] "a" "b" "c" "d" "e"
> fff<-ff[1:2]
> nlevels(fff)
[1] 5

> fff
[1] a b
Levels: a b c d e

Regards
Petr

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of ???
> Sent: Tuesday, January 21, 2014 7:36 AM
> To: r-help at r-project.org
> Subject: [R] how to get the numbers of factors in a matrix
>
> Dear friends,
>
>
> I have a question do not know how to resolve.
>
>
> I have a big matrix composed of different columns (I use N here). A
> column is "species" and another one is "latitudes". Now, I want to know
> how I can get the number of different "latitudes" for every "species".
> I have tried to split the matrix according to species (X<-split(N,
> N\$species) and then use sapply(X, function(m){nlevels(m\$latitudes)}) to
> get that. But the result shows the total factor numbers of "latitudes"
> but not the factor numbers of every species I splitted. Also, I have
> tried to use tapply(N\$latitudes, N\$species, nlevels) to do this. The
> that? Thank you very much!
>
>
> Best regards,
> Yichun
>
>
>
>
>
>
>       [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
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> guide.html
> and provide commented, minimal, self-contained, reproducible code.

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