[FR] add selection argument

[JanMarvin]

Basically I want to be able to pass something analog to which(..., arr.ind = TRUE). This should be possible with
rowcol_to_dims(enforce = TRUE) and/or with wb_dims(enforce = TRUE). The argument enforce is already used in wb_add_data() to indicate that specific dims are requested.

library(openxlsx2)

# create a subset of mtcars
df <- mtcars[14:19, ]

# create coordinates from the which condition df < 4
df_sel <- as.data.frame(which(df < 4, arr.ind = TRUE))

# helper function to create dims out of the condition
rowcol_to_dims2 <- function(row, col) {
  if (length(row) != length(col)) stop("lengths are unequal")
  cols <- int2col(col)
  rows <- as.integer(row)
  cells <- vapply(seq_along(row), function(x) paste0(cols[x], rows[x]), NA_character_)
  paste0(cells, collapse = ",")
}

# create the dims
sel_dims <- rowcol_to_dims2(row = df_sel$row, col = df_sel$col)

dims_to_dataframe(dims = sel_dims, fill = TRUE)
#>    E  F G  H  I  J  K
#> 1 E1 F1   H1 I1 J1 K1
#> 2 E2      H2 I2 J2   
#> 3 E3      H3 I3 J3   
#> 4 E4      H4 I4 J4   
#> 5    F5   H5 I5    K5
#> 6    F6   H6 I6    K6

# use this
wb <- wb_workbook()$add_worksheet()$add_data(x = df, col_names = FALSE)$
  add_fill(dims = sel_dims, color = wb_color("yellow"))

if(interactive()) wb$open()