[R] substitute column data frame based on name stored in variable in r

[Luigi Marongiu]

You are right, vect will contain the names of the columns of the real
dataframe buyt the actual simulation of the real case is more like
this:
```
> df = data.frame(A = 1:5, B = c(1, 2, NA, 2, NA), C = c("value is blue", "Value is red", "empty", "  value is blue", " Value is green"), D = 9:13, E = c("light", "light", "heavy", "heavy", "heavy")); df
  A  B               C  D     E
1 1  1   value is blue  9 light
2 2  2    Value is red 10 light
3 3 NA           empty 11 heavy
4 4  2   value is blue 12 heavy
5 5 NA  Value is green 13 heavy
> vect = LETTERS[1:5]
> df[df[['vect[2]']] == 2, 'vect[2]'] <- "No"; df
  A  B               C  D     E vect[2]
1 1  1   value is blue  9 light    <NA>
2 2  2    Value is red 10 light    <NA>
3 3 NA           empty 11 heavy    <NA>
4 4  2   value is blue 12 heavy    <NA>
5 5 NA  Value is green 13 heavy    <NA>
> df[df[[vect[2]]] == 2, vect[2]] <- "No"; df
Error in `[<-.data.frame`(`*tmp*`, df[[vect[2]]] == 2, vect[2], value = "No") :
  missing values are not allowed in subscripted assignments of data frames
```
but still, I get an extra column instead of working on column B
directly. and I can't dispense the quotation marks...

On Mon, Aug 9, 2021 at 1:31 PM Ivan Krylov <krylov.r00t using gmail.com> wrote:
>
> On Mon, 9 Aug 2021 13:16:02 +0200
> Luigi Marongiu <marongiu.luigi using gmail.com> wrote:
>
> > df = data.frame(VAR = ..., VAL = ...)
> > vect = letters[1:5]
>
> What is the relation between vect and the column names of the data
> frame? Is it your intention to choose rows or columns using `vect`?
>
> > df[df[['vect[2]']] == 2, 'vect[2]']
>
> '...' creates a string literal. If you want to evaluate an R
> expression, don't wrap it in quotes.
>
> I had assumed you wanted to put column names in the vector `vect`, but
> now I'm just confused: `vect` is the same as df$VAR, not colnames(df).
> What do you want to achieve?
>
> Again, you can access the second column with much less typing by
> addressing it directly: df[[2]]
>
> Does it help if you consult [**] or some other tutorial on subsetting
> in R?
>
> --
> Best regards,
> Ivan
>
> [**]
> https://cran.r-project.org/doc/manuals/r-release/R-intro.html#Index-vectors
> https://cran.r-project.org/doc/manuals/r-release/R-intro.html#Lists



-- 
Best regards,
Luigi