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

[PIKAL Petr]

Hi

you could save yourself time to read help page for factor

> -----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 12:09 PM
> 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"?

data.frame is not a matrix

each factor have levels attribute
levels(input$M1)
level 0/0 shall be the first so
levels(input$M1)[1] <-"999/999"

Easiest way is probably cycle through columns of your data

for( i in columns) levels(input[,i])[levels(input[,i])=="0/0"]<-"999/999"

Regards
Petr


> 
> 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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