Have a look at the base functions tapply and aggregate.
For example see:
-
https://cran.r-project.org/doc/manuals/r-release/R-intro.html#The-function-tapply_0028_0029-and-ragged-arrays
,
- https://online.stat.psu.edu/stat484/lesson/9/9.2,
- or ?tapply and ?aggregate.
Also your current code seems to contain an error: `s = df[df$y == i,]`
should be `s = df$z[df$y == i]` I think.
HTH,
Jan
On 17-11-2021 14:20, Luigi Marongiu wrote:
Hello,
I have a dataframe with 3 variables. I want to loop through it to get
the mean value of the variable `z`, as follows:
```
df = data.frame(x = c(rep(1,5), rep(2,5), rep(3,5)),
y = rep(letters[1:5],3),
z = rnorm(15),
stringsAsFactors = FALSE)
m = vector()
for (i in unique(df$y)) {
s = df[df$y == i,]
m = append(m, mean(s$z))
}
names(m) = unique(df$y)
(m)
a b c d e
-0.6355382 -0.4218053 -0.7256680 -0.8320783 -0.2587004
```
The problem is that I have one million `y` values, so the work takes
almost a day. I understand that vectorization will speed up the
procedure. But how shall I write the procedure in vectorial terms?
Thank you
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______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
