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

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?

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entries-of-column-of-type-factor-Adding-a-new-level-to-a-factor-
tp4641402.html
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Changing entries of column of type "factor"/Adding a new level to a factor

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