[R] How do I convert factors to numeric? It's an FAQ but...

[ONKELINX, Thierry]

f is a dataframe of factor, not a factor

use either

as.numeric(levels(f$your.factor))[f$your.factor]

or if f only contains factors

apply(f, 2, function(x){as.numeric(levels(x))[x]})

ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest
team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
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1070 Anderlecht
Belgium
+ 32 2 525 02 51
+ 32 54 43 61 85
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-----Oorspronkelijk bericht-----
Van: r-help-bounces op r-project.org [mailto:r-help-bounces op r-project.org] Namens John Coulthard
Verzonden: vrijdag 13 april 2012 15:08
Aan: r-help op r-project.org
Onderwerp: [R] How do I convert factors to numeric? It's an FAQ but...


Dear R list people

I loaded a file of numbers into R and got a dataframe of factors.  So I tried to convert it to numeric as per the FAQ using as.numeric().  But I'm getting errors (please see example), so what am I getting wrong?

Thanks for your time.
John

Example...

#my data object
> f
   GSM187153 GSM187154 GSM187155 GSM187156 GSM187157 GSM187158 GSM187159
13  7.199346  7.394519  7.466155  8.035864  7.438536  7.308401  7.707994
14  6.910426  6.360291  6.228221   7.42918  7.120322  6.108129  7.201477
15   8.85921  9.152096  9.125067    6.4458  8.600319   8.97577  9.691167
16  5.851665  5.621529  5.673689  6.331274  6.160159   5.65945  5.595156
17  9.905257  8.596643   9.11741  9.872789  8.909299  9.104171  9.158998
18  6.176691  6.429807  6.418132  6.849236  6.162308  6.432743  6.444664
19  7.599871  8.795133  8.382509  5.887119  7.941895  7.666692  8.170374
20  9.458262   8.39701  8.402015    9.0859  8.995632  8.427601  8.265105
21  8.179803  9.868286 10.570601  4.905013  9.488779  9.148336  9.654022
22  7.456822  8.037138  7.953766  6.666418  7.674927  7.995109  7.635158
   GSM187160 GSM187161 GSM187162
13  7.269558  7.537711  7.099806
14   6.61534  7.125821  6.413295
15   8.64715  8.252031  9.445682
16  5.639816    5.9257  5.752994
17  8.856829  9.043991  8.839183
18    6.4307   6.71052    6.5269
19  7.674577  7.390617  8.638025
20  8.132649  8.755642  8.137992
21  9.897561  7.619129 10.242096
22  7.836658  7.297986  8.679438
> class(f)
[1] "data.frame"

#all the columns in the dataframe are of class 'factor'
> for(i in 1:ncol(f)){if(class(f[,i])!="factor"){print(class(f[,i]))}}
>
#but it won't convert to numeric
> g<-as.numeric(as.character(f))
Warning message:
NAs introduced by coercion
> g
 [1] NA NA NA NA NA NA NA NA NA NA
> g<-as.numeric(levels(f))[as.integer(f)]
Error: (list) object cannot be coerced to type 'integer'
>


R version 2.14.1 (2011-12-22)
Copyright (C) 2011 The R Foundation for Statistical Computing ISBN 3-900051-07-0
Platform: i386-redhat-linux-gnu (32-bit)



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