Implement stringr::str_replace_na()

[etiennebacher]

What functionality are you missing?
https://stringr.tidyverse.org/reference/str_replace_na.html

Is this functionality present in the tidyverse or in polars (or both)?
stringr

---

I didn't even know this existed, so I'm unlikely to implement this myself but I think it's a good first issue if someone wants to contribute using the steps detailed in this guide.

Here's the equivalent in Polars (those are simple cases, it would be worth checking the stringr tests for corner cases):

library(polars)
library(stringr)
library(dplyr, warn.conflicts = FALSE)

test_df <- data.frame(x = c(NA, "abc", "def"), y = c(NA, 2, 3))
test_pl <- as_polars_df(test_df)

### tidyverse
# basic
test_df |> 
  mutate(foo = str_replace_na(x))
#>      x  y foo
#> 1 <NA> NA  NA
#> 2  abc  2 abc
#> 3  def  3 def
# coerce values to character
test_df |> 
  mutate(foo = str_replace_na(y))
#>      x  y foo
#> 1 <NA> NA  NA
#> 2  abc  2   2
#> 3  def  3   3

### polars
# basic
test_pl$with_columns(
  foo = pl$col("x")$replace_strict(
    old = NA, new = "NA", default = pl$col("x"), return_dtype = pl$String
  )
)
#> shape: (3, 3)
#> ┌──────┬──────┬─────┐
#> │ x    ┆ y    ┆ foo │
#> │ ---  ┆ ---  ┆ --- │
#> │ str  ┆ f64  ┆ str │
#> ╞══════╪══════╪═════╡
#> │ null ┆ null ┆ NA  │
#> │ abc  ┆ 2.0  ┆ abc │
#> │ def  ┆ 3.0  ┆ def │
#> └──────┴──────┴─────┘
# coerce values to character
test_pl$with_columns(
  foo = pl$col("y")$replace_strict(
    old = NA, new = "NA", default = pl$col("y"), return_dtype = pl$String
  )
)
#> shape: (3, 3)
#> ┌──────┬──────┬─────┐
#> │ x    ┆ y    ┆ foo │
#> │ ---  ┆ ---  ┆ --- │
#> │ str  ┆ f64  ┆ str │
#> ╞══════╪══════╪═════╡
#> │ null ┆ null ┆ NA  │
#> │ abc  ┆ 2.0  ┆ 2.0 │
#> │ def  ┆ 3.0  ┆ 3.0 │
#> └──────┴──────┴─────┘