Join algorithms in dplyr

dcr · November 6, 2023, 4:54pm

Which algorithms does dplyr implement under the hood for performing joins? Does it differ depending on the type of join?

nirgrahamuk · November 6, 2023, 5:45pm

here you go :

github.com

r-lib/vctrs/blob/main/man/faq/internal/matches-algorithm.Rmd

---
output: html_document
editor_options: 
  chunk_output_type: console
---

```{r, child = "../setup.Rmd", include = FALSE}
```

`vec_locate_matches()` is similar to `vec_match()`, but detects _all_ matches by default, and can match on conditions other than equality (like `>=` and `<`). There are also various other arguments to limit or adjust exactly which kinds of matches are returned. Here is an example:

```{r}
x <- c("a", "b", "a", "c", "d")
y <- c("d", "b", "a", "d", "a", "e")

# For each value of `x`, find all matches in `y`
# - The "c" in `x` doesn't have a match, so it gets an NA location by default
# - The "e" in `y` isn't matched by anything in `x`, so it is dropped by default
vec_locate_matches(x, y)
```

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dcr · November 6, 2023, 6:01pm

Thanks! So, is that an implementation of sort-merge?

system · November 27, 2023, 6:02pm

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