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Diffstat (limited to 'docs/doc/pick.html')
| -rw-r--r-- | docs/doc/pick.html | 13 |
1 files changed, 5 insertions, 8 deletions
diff --git a/docs/doc/pick.html b/docs/doc/pick.html index b0e99195..a296d6c0 100644 --- a/docs/doc/pick.html +++ b/docs/doc/pick.html @@ -6,7 +6,7 @@ <div class="nav"><a href="https://github.com/mlochbaum/BQN">BQN</a> / <a href="../index.html">main</a> / <a href="index.html">doc</a></div> <h1 id="pick">Pick</h1> <p>Pick (<code><span class='Function'>⊑</span></code>) chooses elements from <code><span class='Value'>𝕩</span></code> based on <a href="indices.html">index</a> lists from <code><span class='Value'>𝕨</span></code>. <code><span class='Value'>𝕨</span></code> can be a plain list, or even one number if <code><span class='Value'>𝕩</span></code> is a list, in order to get one element from <code><span class='Value'>𝕩</span></code>. It can also be an array of index lists, or have deeper array structure: each index list will be replaced with the element of <code><span class='Value'>𝕩</span></code> at that index, effectively applying to <code><span class='Value'>𝕨</span></code> at <a href="depth.html#the-depth-modifier">depth</a> 1.</p> -<p>With no <code><span class='Value'>𝕨</span></code>, monadic <code><span class='Function'>⊑</span><span class='Value'>𝕩</span></code> takes the first element of <code><span class='Value'>𝕩</span></code> in index order, or its <a href="fill.html">fill element</a> if <code><span class='Value'>𝕩</span></code> is empty (causing an error if no fill is known).</p> +<p>With no <code><span class='Value'>𝕨</span></code>, monadic <code><span class='Function'>⊑</span><span class='Value'>𝕩</span></code> takes the first element of <code><span class='Value'>𝕩</span></code> in index order, with an error if <code><span class='Value'>𝕩</span></code> is empty.</p> <p>While sometimes "scatter-point" indexing is necessary, using Pick to select multiple elements from <code><span class='Value'>𝕩</span></code> is less array-oriented than <a href="select.html">Select</a> (<code><span class='Function'>⊏</span></code>), and probably slower. Consider rearranging your data so that you can select along axes instead of picking out elements.</p> <h2 id="one-element">One element</h2> <p>When the left argument is a number, Pick gets an element from a list:</p> @@ -55,15 +55,12 @@ <span class='Function'>⊑</span> <span class='Function'>↕</span><span class='Number'>4</span><span class='Ligature'>‿</span><span class='Number'>2</span><span class='Ligature'>‿</span><span class='Number'>5</span><span class='Ligature'>‿</span><span class='Number'>1</span> ⟨ 0 0 0 0 ⟩ </pre> -<p>If <code><span class='Value'>𝕩</span></code> is empty then Pick always results in an error. First never gives an error: instead it returns the <a href="fill.html">fill element</a> for <code><span class='Value'>𝕩</span></code>.</p> -<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=4oqRICIiCuKKkSDiiaLPgAriipEgMOKGkTzin6giICAiLOKGlTTin6k=">↗️</a><pre> <span class='Function'>⊑</span> <span class='String'>""</span> -' ' +<p>If <code><span class='Value'>𝕩</span></code> is empty then First results in an error, like Pick.</p> +<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=4oqRICIiCuKKkSDiiaLPgA==">↗️</a><pre> <span class='Function'>⊑</span> <span class='String'>""</span> +ERROR <span class='Function'>⊑</span> <span class='Function'>≢</span><span class='Number'>π</span> -0 - <span class='Function'>⊑</span> <span class='Number'>0</span><span class='Function'>↑<</span><span class='Bracket'>⟨</span><span class='String'>" "</span><span class='Separator'>,</span><span class='Function'>↕</span><span class='Number'>4</span><span class='Bracket'>⟩</span> -⟨ " " ⟨ 0 0 0 0 ⟩ ⟩ +ERROR </pre> -<p>So one way to find the fill element for an array <code><span class='Value'>𝕩</span></code> of any shape is <code><span class='Function'>⊑</span><span class='Number'>0</span><span class='Function'>⥊</span><span class='Value'>𝕩</span></code>.</p> <p>In APL it's common to get the last element of a list with an idiom that translates to <code><span class='Function'>⊑⌽</span></code>, or First-<a href="reverse.html">Reverse</a>. In BQN the most straightforward way is to select with index <code><span class='Number'>¯1</span></code> instead. I also sometimes use <a href="fold.html">Fold</a> with the Right <a href="identity.html">identity function</a>.</p> <a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=4oqR4oy9ICJsYXN0IgrCrzHiipEgImxhc3QiCuKKosK0ICJsYXN0Ig==">↗️</a><pre> <span class='Function'>⊑⌽</span> <span class='String'>"last"</span> 't' |