List Iteration

piter() iterates over an arbitrary number of list elements evaluating identically indexed components and is an analogue to purrr::pmap() without loading the purrr namespace. liter() is a thin wrapper around mapply() intended specifically for paired .x and .y values (similar to purrr::map2()). If .y is missing and .x is named, this is equal to liter(.x, names(.x), ...), which is the behavior of purrr::imap(). Both piter() and liter() support the formula construction (~).

Usage

liter(.x, .y = NULL, .f, ...)

piter(.l, .f, ...)

Arguments

.x, .y

Vectors or objects of the same length.

.f

A function to be applied to each element of x.

...

Additional arguments passed to .f.

.l

A named list of elements, each to iterate over. Must have the same length. Also supports a data frame, whose rows will iterate over using names as parameters.

Value

Both functions always return a list, sometimes named if possible by rules similar to sapply().

Functions

• piter(): piter() iterates over a named list of identical lengths.

Examples

x <- LETTERS
names(x) <- letters
liter(x, 1:26, paste, sep = "-") |> head()
#> $a
#> [1] "A-1"
#> 
#> $b
#> [1] "B-2"
#> 
#> $c
#> [1] "C-3"
#> 
#> $d
#> [1] "D-4"
#> 
#> $e
#> [1] "E-5"
#> 
#> $f
#> [1] "F-6"
#> 

# .y = NULL; uses names(.x)
liter(x, .f = paste, sep = "-") |> head()
#> $a
#> [1] "A-a"
#> 
#> $b
#> [1] "B-b"
#> 
#> $c
#> [1] "C-c"
#> 
#> $d
#> [1] "D-d"
#> 
#> $e
#> [1] "E-e"
#> 
#> $f
#> [1] "F-f"
#> 

# .y = index 1:3
liter(c("a", "b" , "c"), .f = paste, sep = "=")
#> $a
#> [1] "a=1"
#> 
#> $b
#> [1] "b=2"
#> 
#> $c
#> [1] "c=3"
#> 

# anonymous on-the-fly .f()
v <- rnorm(6)
liter(1:6, v, function(a, b) a + b^2) |> unlist()
#> [1] 1.173273 2.013003 3.004086 4.845172 5.812405 6.636370

# if .y is explicit; formula syntax
# must use `.x` and `.y` in formula
liter(1:6, v, ~ .x + .y^2) |> unlist()
#> [1] 1.173273 2.013003 3.004086 4.845172 5.812405 6.636370

piter(list(a = head(LETTERS), b = head(letters)), function(a, b) paste0(a, b)) |>
  unlist()
#>    A    B    C    D    E    F 
#> "Aa" "Bb" "Cc" "Dd" "Ee" "Ff" 

# supports ~formula syntax
piter(list(a = head(LETTERS), b = head(letters)), ~ paste0(a, b)) |> unlist()
#>    A    B    C    D    E    F 
#> "Aa" "Bb" "Cc" "Dd" "Ee" "Ff" 

# supports data frames
df <- data.frame(a = head(LETTERS), b = rev(tail(letters)))
piter(df, ~ paste0(a, b)) |> unlist()
#>    A    B    C    D    E    F 
#> "Az" "By" "Cx" "Dw" "Ev" "Fu"