ianmcook commented on a change in pull request #10327:
URL: https://github.com/apache/arrow/pull/10327#discussion_r636523993
##########
File path: r/R/expression.R
##########
@@ -76,7 +76,15 @@
Expression <- R6Class("Expression", inherit = ArrowObject,
public = list(
ToString = function() compute___expr__ToString(self),
- type = function(schema) compute___expr__type(self, schema),
+ schema = NULL,
+ bind = function(schema) self$schema <- schema,
+ type = function() {
+ if (is.null(self$schema)) {
+ stop("Must bind() expression to a schema before returning its type",
call. = FALSE)
+ }
+ compute___expr__type(self, self$schema)
Review comment:
Just for posterity, here's the test code I ran
```r
library(dplyr)
library(arrow)
x <- as.data.frame(t(c(1:26)))
colnames(x) <- letters
x$z <- "z"
x <- Table$create(x)
start_time <- Sys.time()
for (i in 1:100) {
q <- x %>% relocate(where(is.numeric), .after = where(is.character))
w <- x %>% relocate(where(is.character), .before = where(is.numeric))
}
end_time <- Sys.time()
end_time - start_time
# ~8 seconds before change
# ~4 seconds after change
```
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