Replacing values of data.frame

Question

I found multiple post on internet however, I'm still not able to remplace the "?" value by "-1" as asked by my teacher. This is my code:

>library(e1071);

>mammogram <- data.frame

>mammogram.frame = read.table("https://archive.ics.uci.edu/ml/machine-learning-databases/mammographic-masses/mammographic_masses.data",  
            sep=",", 
            col.names=c("Birads","Age","Shape","Margin","Density","Severity"), 
            fill=TRUE, 
            strip.white=TRUE)

>mammogram.frame[which(mammogram.frame=="?")]<-"-1"

>mammogram.frame

>summary(mammogram.frame)

>svm.model <- svm(Density~.,
    data=mammogram.frame,
    type="C-classification",
    cost=1.0,
    kernel="polynomial",
    degree=2.0)
>svm.model

and when I run the code, the mammogram.frame[which(mammogram.frame=="?")]<-"-1" return the following output:

> mammogram.frame[which(mammogram.frame=="?")]<-"-1"
Error in `[<-.data.frame`(`*tmp*`, which(mammogram.frame == "?"), value = "-1") : 
  new columns would leave holes after existing columns

I also tried the code below but it transform my data in something else...

> mammogram.frame <- as.character(mammogram.frame)
> mammogram.frame[mammogram.frame == "?"] <- "-1"

> mammogram.frame
[1] "c(6, 5, 6, 5, 6, 5, 5, ...)

> mammogram.frame <- as.factor(mammogram.frame)
> mammogram.frame
[1] c(6, 5, 6, 5, 6, 5, 5, ...)

I mean by that that it doesn't give my the same visual as the beginning when I run >mammogram.frame..

Any idea to passe the "?" value to -1? because it works when I do >mammogram.frame[which(mammogram.frame=="?")] <- NA

Thank !

score 0 · Answer 1 · answered Feb 10 '17 at 05:29

Try the following change when loading:

mammogram.frame = read.table("https://archive.ics.uci.edu/ml/machine-learning-databases/mammographic-masses/mammographic_masses.data",  
                             sep=",", 
                             col.names=c("Birads","Age","Shape","Margin","Density","Severity"), 
                             fill=TRUE, 
                             strip.white=TRUE,
                             stringsAsFactors = F)

And then do:

mammogram.frame[mammogram.frame=="?"] = "-1"

Result:

> head(mammogram.frame)
  Birads Age Shape Margin Density Severity
1      5  67     3      5       3        1
2      4  43     1      1      -1        1
3      5  58     4      5       3        1
4      4  28     1      1       3        0
5      5  74     1      5      -1        1
6      4  65     1     -1       3        0

Replacing values of data.frame

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