Using dplyr functions inside apply - r

Question

I want to use dplyr functions inside apply, to every element of a matrix (BRCK), which is a matrix of dataframes.
I tried something like this:
apply(BRCK, c(1,2), function(x) dplyr::select(x, dplyr::contains("_01_"), 1) %>%
dplyr::filter((month(`BRCK[[la, lo]]`) == 1)) %>%
dplyr::select(-contains("BRCK"))
But it returns
Error: Variable context not set
And the traceback:
13. stop(cnd)
12. abort("Variable context not set")
11. cur_vars_env$selected %||% abort("Variable context not set")
10. current_vars()
9. tolower(vars)
8. dplyr::contains("_01_")
7. select.list(x, dplyr::contains("_01_"), 1)
6. dplyr::select(x, dplyr::contains("_01_"), 1)
5. eval(lhs, parent, parent)
4. eval(lhs, parent, parent)
3. dplyr::select(x, dplyr::contains("_01_"), 1) %>% dplyr::filter(x,
(month(`BRCK[[la, lo]]`) == 1)) %>% dplyr::select(x, -contains("BRCK"))
2. FUN(newX[, i], ...)
1. apply(BRCK, c(1, 2), function(x) dplyr::select(x, dplyr::contains("_01_"), 1) %>% dplyr::filter(x, (month(`BRCK[[la, lo]]`) == 1)) %>%
dplyr::select(x, -contains("BRCK")))
BRCK is a very large object, It works with for cycles but I'm trying to replace them with apply functions.

Answer 1

With apply, x is passed as a list in the function and dplyr only deals with dataframe.
apply(BRCK, c(1,2), is.data.frame)
[,1] [,2] [,3]
[1,] FALSE FALSE FALSE
[2,] FALSE FALSE FALSE
[3,] FALSE FALSE FALSE
but :
apply(BRCK, c(1,2), function(x) is.data.frame(x[[1]]))
[,1] [,2] [,3]
[1,] TRUE TRUE TRUE
[2,] TRUE TRUE TRUE
[3,] TRUE TRUE TRUE
so :
library(tidyverse)
apply(BRCK, c(1,2),
function(x) {
x[[1]] %>%
dplyr::select(dplyr::contains("_01_"), 1) %>%
dplyr::filter(lubridate::month(`BRCK[[la, lo]]`) == 1) %>%
dplyr::select(-contains("BRCK"))
}
)

Answer 2

One problem is that each element in the loop is a list of a single data frame, not an actual data frame. Compare:
apply(BRCK, c(1,2), function(x) {
class(x)
})
[,1] [,2] [,3]
[1,] "list" "list" "list"
[2,] "list" "list" "list"
[3,] "list" "list" "list"
apply(BRCK, c(1,2), function(x) {
class(x[[1]])
})
[,1] [,2] [,3]
[1,] "data.frame" "data.frame" "data.frame"
[2,] "data.frame" "data.frame" "data.frame"
[3,] "data.frame" "data.frame" "data.frame"
I would suggest not using apply loop (rather use lapply on the indices) since the way apply subsets objects and modifies them is not well documented.
I would also suggest not storing data.frames in a matrix. You could store them in a list, and set attributes for the metadata that is implied by the matrix indices.