[R] How to modify rows matching patter on multiple columns of dataframe?

[Eric Berger]

Hi Luigi,
I would take a slightly different approach. Maybe this is helpful.

idV <- grep("var[123]",colnames(df))
df[,idV][df[,idV]=="a"] <- "z"

df
  var1 var2 var3 var4  var5
1    z    A    z    1 light
2    b    B    b    4 light
3    c    C    c    9 heavy
4    z    D    z   16 heavy
5    b    E    b   25 heavy
6    c    F    c   36 light
7    d    G    d   49 heavy

HTH,
Eric


On Thu, Aug 12, 2021 at 3:38 PM Luigi Marongiu <marongiu.luigi using gmail.com>
wrote:

> Helo
> I have a dataframe whose names are similar and I would like to change
> the rows containing given values simultaneously.
> I can select the columns using library(dplyr) but I can't modify the data:
> ```
> library(dplyr)
> > df <- data.frame(var1 = c(letters[1:3], letters[1:4]),
> +                 var2 = c(LETTERS[1:7]),
> +                 var3 = c(letters[1:3], letters[1:4]),
> +                 var4 = (1:7)^2,
> +                 var5 = c("light", "light", "heavy", "heavy", "heavy",
> +                          "light", "heavy"),
> +                 stringsAsFactors = FALSE); df
>   var1 var2 var3 var4  var5
> 1    a    A    a    1 light
> 2    b    B    b    4 light
> 3    c    C    c    9 heavy
> 4    a    D    a   16 heavy
> 5    b    E    b   25 heavy
> 6    c    F    c   36 light
> 7    d    G    d   49 heavy
> > select(df, matches("var[123]"))
>   var1 var2 var3
> 1    a    A    a
> 2    b    B    b
> 3    c    C    c
> 4    a    D    a
> 5    b    E    b
> 6    c    F    c
> 7    d    G    d
> > df[[select(df, matches("var[123]")) == "a"]] <- "z"
> Error in `[[<-`(`*tmp*`, i, value = value) :
>   recursive indexing failed at level 2
> > df[[select(df, contains("var1")) == "a"]] <- "z"
> Error in `[[<-`(`*tmp*`, i, value = value) :
>   recursive indexing failed at level 2
> ```
> If I sue which, I get a wrong substitution :
> ```
> > df[which(select(df, matches("var[123]")) == "a"), ] <- "z"; df
>    var1 var2 var3 var4  var5
> 1     z    z    z    z     z
> 2     b    B    b    4 light
> 3     c    C    c    9 heavy
> 4     z    z    z    z     z
> 5     b    E    b   25 heavy
> 6     c    F    c   36 light
> 7     d    G    d   49 heavy
> 8  <NA> <NA> <NA> <NA>  <NA>
> 9  <NA> <NA> <NA> <NA>  <NA>
> 10 <NA> <NA> <NA> <NA>  <NA>
> 11 <NA> <NA> <NA> <NA>  <NA>
> 12 <NA> <NA> <NA> <NA>  <NA>
> 13 <NA> <NA> <NA> <NA>  <NA>
> 14 <NA> <NA> <NA> <NA>  <NA>
> 15    z    z    z    z     z
> 16 <NA> <NA> <NA> <NA>  <NA>
> 17 <NA> <NA> <NA> <NA>  <NA>
> 18    z    z    z    z     z
> ```
>
> what is the correct syntax?
> Thank you
>
> --
> Best regards,
> Luigi
>
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