[R] Changing entries of column of type "factor"/Adding a new level to a factor

[William Dunlap]

One way is to read in your text data as character columns with
read.table(stringsAsFactors=FALSE,...), then fiddle with the values,
and finally make factors out of the columns that  you want to be factors,
specifying the levels explicitly.  (Do you really want those number/number
things to be treated as factors?  The orders of their levels will be weird unless
you list them all when making the factor.)

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of Fridolin
> Sent: Monday, August 27, 2012 3:09 AM
> To: r-help at r-project.org
> Subject: [R] Changing entries of column of type "factor"/Adding a new level to a factor
> 
> What is a smart way to change an entry inside a column of a dataframe or
> matrix which is of type "factor"?
> 
> Here is my script incl. input data:
> > #set working directory:
> > setwd("K:/R")
> >
> > #read in data:
> > input<-read.table("Exampleinput.txt", sep="\t", header=TRUE)
> >
> > #check data:
> > input
>    Ind      M1      M2      M3
> 1    1   96/98 120/120     0/0
> 2    2 102/108 120/124 305/305
> 3    3  96/108 120/120     0/0
> 4    4     0/0 116/120 300/305
> 5    5  96/108 120/130 300/305
> 6    6   98/98 116/120 300/305
> 7    7  98/108 120/120 305/305
> 8    8  98/108 120/120 305/305
> 9    9  98/102 120/124 300/300
> 10  10 108/108 120/120 305/305
> > str(input)
> 'data.frame':	10 obs. of  4 variables:
>  $ Ind: int  1 2 3 4 5 6 7 8 9 10
>  $ M1 : Factor w/ 8 levels "0/0","102/108",..: 5 2 4 1 4 8 7 7 6 3
>  $ M2 : Factor w/ 4 levels "116/120","120/120",..: 2 3 2 1 4 1 2 2 3 2
>  $ M3 : Factor w/ 4 levels "0/0","300/300",..: 1 4 1 3 3 3 4 4 2 4
> >
> > #replace 0/0 by 999/999:
> > for (r in 1:10)
> +   for (c in 2:4)
> +     if (input[r,c]=="0/0") input[r,c]<-"999/999"
> Warnmeldungen:
> 1: In `[<-.factor`(`*tmp*`, iseq, value = "999/999") :
>   invalid factor level, NAs generated
> 2: In `[<-.factor`(`*tmp*`, iseq, value = "999/999") :
>   invalid factor level, NAs generated
> 3: In `[<-.factor`(`*tmp*`, iseq, value = "999/999") :
>   invalid factor level, NAs generated
> > input
>    Ind      M1      M2      M3
> 1    1   96/98 120/120    <NA>
> 2    2 102/108 120/124 305/305
> 3    3  96/108 120/120    <NA>
> 4    4    <NA> 116/120 300/305
> 5    5  96/108 120/130 300/305
> 6    6   98/98 116/120 300/305
> 7    7  98/108 120/120 305/305
> 8    8  98/108 120/120 305/305
> 9    9  98/102 120/124 300/300
> 10  10 108/108 120/120 305/305
> 
> 
> I want to replace all "0/0" by "999/999". My code should work for columns of
> type "character" and "integer". But to make it work for a "factor"-column I
> would need to add the new level of "999/999" at first, I guess. How do I add
> a new level?
> 
> 
> 
> --
> View this message in context: http://r.789695.n4.nabble.com/Changing-entries-of-
> column-of-type-factor-Adding-a-new-level-to-a-factor-tp4641402.html
> Sent from the R help mailing list archive at Nabble.com.
> 
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