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

[Kimmo Elo]

Hi,

something like this (a customised version based on this: 
https://stackoverflow.com/questions/25768305/r-replace-multiple-values-in-multiple-columns-of-dataframes-with-na
):

--- snip ---

col_idx<-grep("^var[123]", names(df))
m1<-as.matrix(df[,col_idx])
m1[m1=="a"]<-"z"
df[col_idx]<-m1
df

--- snip ---

HTH,

Kimmo

to, 2021-08-12 kello 14:37 +0200, Luigi Marongiu kirjoitti:
> 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
>