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Diffstat (limited to 'doc/pick.md')
| -rw-r--r-- | doc/pick.md | 7 |
1 files changed, 2 insertions, 5 deletions
diff --git a/doc/pick.md b/doc/pick.md index 9b014796..092f87ed 100644 --- a/doc/pick.md +++ b/doc/pick.md @@ -4,7 +4,7 @@ Pick (`⊑`) chooses elements from `𝕩` based on [index](indices.md) lists from `𝕨`. `𝕨` can be a plain list, or even one number if `𝕩` is a list, in order to get one element from `𝕩`. It can also be an array of index lists, or have deeper array structure: each index list will be replaced with the element of `𝕩` at that index, effectively applying to `𝕨` at [depth](depth.md#the-depth-modifier) 1. -With no `𝕨`, monadic `⊑𝕩` takes the first element of `𝕩` in index order, or its [fill element](fill.md) if `𝕩` is empty (causing an error if no fill is known). +With no `𝕨`, monadic `⊑𝕩` takes the first element of `𝕩` in index order, with an error if `𝕩` is empty. While sometimes "scatter-point" indexing is necessary, using Pick to select multiple elements from `𝕩` is less array-oriented than [Select](select.md) (`⊏`), and probably slower. Consider rearranging your data so that you can select along axes instead of picking out elements. @@ -44,13 +44,10 @@ With no left argument, `⊑` is called First, and performs a slight generalizati ⊑ "First" ⊑ ↕4‿2‿5‿1 -If `𝕩` is empty then Pick always results in an error. First never gives an error: instead it returns the [fill element](fill.md) for `𝕩`. +If `𝕩` is empty then First results in an error, like Pick. ⊑ "" ⊑ ≢π - ⊑ 0↑<⟨" ",↕4⟩ - -So one way to find the fill element for an array `𝕩` of any shape is `⊑0⥊𝕩`. In APL it's common to get the last element of a list with an idiom that translates to `⊑⌽`, or First-[Reverse](reverse.md). In BQN the most straightforward way is to select with index `¯1` instead. I also sometimes use [Fold](fold.md) with the Right [identity function](identity.md). |