Thank you all for the responses, these are the insights I was hoping for.
There are many ways to get this right, and I happened to run into one that
has a glitch. I see from Luke's explanation how the strange output came
about. Glad to hear that this bug/behavior is already known.
On Fri, Jun 19,
On 6/19/2020 5:49 AM, Sébastien Lahaie wrote:
I ran into some strange behavior in R when trying to assign a treatment to
rows in a data frame. I'm wondering whether any R experts can explain
what's going on.
First, let's assign a treatment to 3 out of 10 rows as follows.
df <- data.frame(unit =
It is a bug that has been present in R since at least R-2.14.0 (the oldest
that I have installed on my laptop).
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Fri, Jun 19, 2020 at 10:37 AM Rui Barradas wrote:
> Hello,
>
>
> Thanks, I hadn't thought of that.
>
> But, why? Is it evaluated once
Hello,
Thanks, I hadn't thought of that.
But, why? Is it evaluated once before assignment and a second time when
the assignment occurs?
To trace both sample and `[<-` gives 2 calls to sample.
trace(sample)
trace(`[<-`)
df[sample(nrow(df), 3),]$treated <- TRUE
trace: sample(nrow(df), 3)
tra
The first subscript argument is getting evaluated twice.
> trace(sample)
> set.seed(2020); df[i<-sample(10,3), ]$Treated <- TRUE
trace: sample(10, 3)
trace: sample(10, 3)
> i
[1] 1 10 4
> set.seed(2020); sample(10,3)
trace: sample(10, 3)
[1] 7 6 8
> sample(10,3)
trace: sample(10, 3)
[1] 1 10 4
Hello,
I don't have an answer on the reason why this happens but it seems like
a bug. Where?
In which of `[<-.data.frame` or `[<-.default`?
A solution is to subset and assign the vector:
set.seed(2020)
df2 <- data.frame(unit = 1:10)
df2$treated <- FALSE
df2$treated[sample(nrow(df2), 3)] <
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