[help] map on a list passes list elements to the command.

[eliocamp]

Help

• I understand and agree to https://books.ropensci.org/targets/help.html.

Description

lapply, map, etc.. pass a vector argument to the function

vector <- 1:3
list <- as.list(vector)
vapply(list, is.list, FUN.VALUE = logical(1))
#> [1] FALSE FALSE FALSE

In targets, map passes each elements as a one-length list

targets::tar_dir({ 
  targets::tar_script({

    list(
      targets::tar_target(paths_list, as.list(1:3)),
      
      targets::tar_target(
        x,
        is.list(paths_list),
        pattern = map(paths_list)
      )
    )
  })
  targets::tar_make()

  targets::tar_read(x)

})
#> ▶ dispatched target paths_list
#> ● completed target paths_list [0.001 seconds]
#> ▶ dispatched branch x_0a69e4b5
#> ● completed branch x_0a69e4b5 [0 seconds]
#> ▶ dispatched branch x_fe432996
#> ● completed branch x_fe432996 [0.001 seconds]
#> ▶ dispatched branch x_57ce207a
#> ● completed branch x_57ce207a [0 seconds]
#> ● completed pattern x
#> ▶ completed pipeline [0.118 seconds]
#> x_0a69e4b5 x_fe432996 x_57ce207a 
#>       TRUE       TRUE       TRUE

To get the equivalent, you need to extract the element

targets::tar_dir({
  targets::tar_script({
    
    list(
      targets::tar_target(paths_list, as.list(1:3)),
      
      targets::tar_target(
        x,
        is.list(paths_list[[1]]),
        pattern = map(paths_list)
      )
    )
  })
  targets::tar_make()
  
  targets::tar_read(x)
  
})
#> ▶ dispatched target paths_list
#> ● completed target paths_list [0.001 seconds]
#> ▶ dispatched branch x_0a69e4b5
#> ● completed branch x_0a69e4b5 [0 seconds]
#> ▶ dispatched branch x_fe432996
#> ● completed branch x_fe432996 [0.001 seconds]
#> ▶ dispatched branch x_57ce207a
#> ● completed branch x_57ce207a [0.001 seconds]
#> ● completed pattern x
#> ▶ completed pipeline [0.117 seconds]
#> x_0a69e4b5 x_fe432996 x_57ce207a 
#>      FALSE      FALSE      FALSE

I expected map to apply the command to each element of paths_list (like extracted with [[]]).
Is this intentional? It's a bit counter-intuitive for me.

[Aariq]

What happens if you set iteration = "list" ?

[eliocamp]

Still a list, weirdly.

targets::tar_dir({ 
  targets::tar_script({

    list(
      targets::tar_target(paths_list, as.list(1:3)),
      
      targets::tar_target(
        x,
        is.list(paths_list),
        pattern = map(paths_list),
        iteration = "list"
      )
    )
  })
  targets::tar_make()

  targets::tar_read(x)

})
#> ▶ dispatched target paths_list
#> ● completed target paths_list [0.001 seconds]
#> ▶ dispatched branch x_0a69e4b5
#> ● completed branch x_0a69e4b5 [0 seconds]
#> ▶ dispatched branch x_fe432996
#> ● completed branch x_fe432996 [0 seconds]
#> ▶ dispatched branch x_57ce207a
#> ● completed branch x_57ce207a [0 seconds]
#> ● completed pattern x
#> ▶ completed pipeline [0.181 seconds]
#> $x_0a69e4b5
#> [1] TRUE
#> 
#> $x_fe432996
#> [1] TRUE
#> 
#> $x_57ce207a
#> [1] TRUE

^{Created on 2024-01-25 with reprex v2.0.2}

[wlandau]

paths_list is a non-dynamic target you are branching over, and specific elements of paths_list are extracted for x using vctrs::vec_slice(). It makes flexible and convenient decisions based on what kind of object you are slicing.

vctrs::vec_slice(letters, 2)
#> [1] "b"

vctrs::vec_slice(as.list(letters), 2)
#> [[1]]
#> [1] "b"

vctrs::vec_slice(mtcars, 2)
#>               mpg cyl disp  hp drat    wt  qsec vs am gear carb
#> Mazda RX4 Wag  21   6  160 110  3.9 2.875 17.02  0  1    4    4

[eliocamp]

Ah, sorry, I had misunderstood how the iteration argument worked. I though it determined how the pattern did the iteration, but instead is a property of how will the target be iterated with map.

This now works.

targets::tar_dir({ 
  targets::tar_script({
    
    list(
      targets::tar_target(paths_list, as.list(1:3), iteration = "list"),
      
      targets::tar_target(
        x,
        is.list(paths_list),
        pattern = map(paths_list)
      )
    )
  })
  targets::tar_make()
  
  targets::tar_read(x)
  
})
#> ▶ dispatched target paths_list
#> ● completed target paths_list [0.001 seconds]
#> ▶ dispatched branch x_bed6a16d
#> ● completed branch x_bed6a16d [0.001 seconds]
#> ▶ dispatched branch x_36a089b4
#> ● completed branch x_36a089b4 [0 seconds]
#> ▶ dispatched branch x_5d98722e
#> ● completed branch x_5d98722e [0 seconds]
#> ● completed pattern x
#> ▶ completed pipeline [0.116 seconds]
#> x_bed6a16d x_36a089b4 x_5d98722e 
#>      FALSE      FALSE      FALSE

^{Created on 2024-01-26 with reprex v2.0.2}

[wlandau]

iteration controls splitting for non-dynamic targets and aggregation for dynamic branches. I rewrite part of the dynamic branching chapter to hopefully explain this better: ropensci-books/targets@22786c8. The manual is currently re-rendering.