What are you actually trying to do here? For the example you give, I would just
sample the index and apply it to both vectors:
ix <- sample(1:20, 5)
df2 <-data.frame(x=df1$x[ix], z=df1$z[ix])
(or even df2 <- df1[ix, c("x","z")] )
If it is something else, you are trying to achieve, it would seem that you rely
on df1$x not having duplicates or you might have an assignment between
incompatible vectors in the for loop.
-pd
> On 20 Jan 2026, at 11.25, Luigi Marongiu <[email protected]> wrote:
>
> Dear all,
> this is a basic question but I could not find a specific answer online.
> I have a dataframe (df1) with, in particular, an identification value
> `x` and an output value `z`.
> I also have another dataframe (df2) that shares `x`.
> I need to assign `z` to df2 where df1$x is equal to df2$x.
> What would be a straightforward way of doing this?
> I can do it, but selecting one element at a time, checking the
> identity of the x elements, and then assigning z. There should be a
> more R way...
> Thank you
>
>
> ```
> df1 = data.frame(x = 1:20,
> y = rep(letters[1:5],4),
> w = c(rep(LETTERS[1],10), rep(LETTERS[2],10)),
> z = rnorm(20),
> stringsAsFactors = FALSE)
> df2 = data.frame(x = sample(df1$x, 5))
> df2$z = NA
> for (i in df1$x) {
> df2$z[df2$x==i] = df1[df1$x==i,]$z
> }
> ```
>
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--
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: [email protected] Priv: [email protected]
______________________________________________
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PLEASE do read the posting guide https://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
