[Bioc-devel] Applying "class" function to columns of a data.frame always return character

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Hello,

I need to identify which columns from a data.frame is a factor. Since I
need to test "is.factor" for all columns, I tried the following code:

apply(dataframe, 2, is.factor)

But it always returned FALSE. Then I tried to check the classes of those
columns using:

apply(dataframe, 2, class)

And it always returned "character". Is the related to the fact that apply
function should be applied to arrays or matrixes, and not to data.frames?

So I believe that apply function convert the data.frame into a matrix. And
the class of the matrix will be character if any of its elements is not
numeric.

So, if I my conclusion about apply function is correct, this is not the way
I should proceed. So, how can I get a vector of booleans as result of some
function applied to columns of a data.frame, e.g., is.factor?
A data frame is a list of equal length vectors, so you can use

    sapply(df, class)
    class(df[["some_column"]]
    class(df$some_column)

Martin
Thanks!

Cheers,

Jo?o Daniel
UFMG - Brazil

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Computational Biology
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Telephone: 206 667-2793
This would work:

sapply(1:ncol(dataframe),function(i,df){
	is.factor(df[,i])
},dataframe)

Cheers,

---------------------------------------------------------------
Nicolas Delhomme

Genome Biology Computational Support

European Molecular Biology Laboratory

Tel: +49 6221 387 8310
Email: nicolas.delhomme at embl.de
Meyerhofstrasse 1 - Postfach 10.2209
69102 Heidelberg, Germany
---------------------------------------------------------------

Hello,

I need to identify which columns from a data.frame is a factor. Since I
need to test "is.factor" for all columns, I tried the following code:

apply(dataframe, 2, is.factor)

But it always returned FALSE. Then I tried to check the classes of those
columns using:

apply(dataframe, 2, class)

And it always returned "character". Is the related to the fact that apply
function should be applied to arrays or matrixes, and not to data.frames?

So I believe that apply function convert the data.frame into a matrix. And
the class of the matrix will be character if any of its elements is not
numeric.

So, if I my conclusion about apply function is correct, this is not the way
I should proceed. So, how can I get a vector of booleans as result of some
function applied to columns of a data.frame, e.g., is.factor?

Thanks!

Cheers,

Jo?o Daniel
UFMG - Brazil

	[[alternative HTML version deleted]]

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