Sam Albers created ARROW-8118:
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Summary: dim method for FileSystemDataset
Key: ARROW-8118
URL: https://issues.apache.org/jira/browse/ARROW-8118
Project: Apache Arrow
Issue Type: Improvement
Components: R
Reporter: Sam Albers
I been using this function enough that I wonder if a) would be useful in the
package and b) whether this is something you think is worth working on. The
basic problem is that if you have a hierarchical file structure that
accommodates using open_dataset, it is definitely useful to know the amount of
data you are dealing with. My idea is that 'FileSystemDataset' would have dim,
nrow and ncol methods. Here is how I've been using it:
{code:java}
library(arrow)
x <- open_dataset("data/rivers-data/", partitioning = c("prov", "month"))
dim_arrow <- function(x) {
rows <- sum(purrr::map_dbl(x$files,
~ParquetFileReader$create(.x)$ReadTable()$num_rows))
cols <- x$schema$num_fields
c(rows, cols)
}
dim_arrow(x)
#> [1] 426929 7
{code}
Ideally this would work on arrow_dplyr_query objects as well but I haven't
quite figured out how that filters based on the partitioning variables.
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