mikerspencer opened a new issue, #39004:
URL: https://github.com/apache/arrow/issues/39004
### Describe the bug, including details regarding any error messages,
version, and platform.
When making evaluations like checking for NA the altrep datatype slows
calculation by approx four times. Tested in arrow 10, 12 & 14 on Ubuntu.
```
library(arrow)
library(dplyr)
# generate data
x = runif(29500000) * 10
d = data.frame(cv = x)
write_dataset(d, "/tmp/data.arrow")
# then read back
df = open_dataset("/tmp/data.arrow/") %>% select(cv) %>% collect()
x = df$cv
y = x + 0
identical(x, y)
microbenchmark::microbenchmark(x={sum(is.na(x))}, y={sum(is.na(y))})
```
Results:
Unit: milliseconds
| expr | min | lq | mean | median | uq | max neval |
|---|---|---|---|---|---|---|
|x | 291.8 | 302.2 | 348.8 | 310.2 | 348.8 | 754.8 | 100 |
| y | 85.3 | 87.2 | 108.8 | 89.3 | 133.4 | 225.4 | 100 |
With thanks to Barry for the reprex
https://mastodon.scot/@[email protected]/111450704657241188
### Component(s)
R
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