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Diffstat (limited to 'docs/doc/pick.html')
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1 files changed, 7 insertions, 6 deletions
diff --git a/docs/doc/pick.html b/docs/doc/pick.html index 275b623a..060dcdc1 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">github</a>) / <a href="../index.html">BQN</a> / <a href="index.html">doc</a></div> <h1 id="pick"><a class="header" href="#pick">Pick</a></h1> <p>Pick (<code><span class='Function'>β</span></code>) chooses elements from <code><span class='Value'>π©</span></code> based on <a href="indices.html">index</a> lists from <code><span class='Value'>π¨</span></code>. <code><span class='Value'>π¨</span></code> can be a plain list, or even one number if <code><span class='Value'>π©</span></code> is a list, in order to get one element from <code><span class='Value'>π©</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'>π©</span></code> at that index, effectively applying to <code><span class='Value'>π¨</span></code> at <a href="depth.html#the-depth-modifier">depth</a> 1.</p> -<p>With no <code><span class='Value'>π¨</span></code>, monadic <code><span class='Function'>β</span><span class='Value'>π©</span></code> takes the first element of <code><span class='Value'>π©</span></code> in index order, with an error if <code><span class='Value'>π©</span></code> is empty.</p> +<p>The one-argument form is called First, and <code><span class='Function'>β</span><span class='Value'>π©</span></code> takes the first element of <code><span class='Value'>π©</span></code> in index order, with an error if <code><span class='Value'>π©</span></code> is empty.</p> <p>While sometimes "scatter-point" indexing is necessary, using Pick to select multiple elements from <code><span class='Value'>π©</span></code> is less array-oriented than <a href="select.html">Select</a> (<code><span class='Function'>β</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"><a class="header" href="#one-element">One element</a></h2> <p>When the left argument is a number, Pick gets an element from a list:</p> @@ -23,7 +23,7 @@ <span class='Number'>Β―2</span> <span class='Function'>β</span> <span class='String'>"abc"</span> 'b' </pre> -<p>Making <code><span class='Value'>π©</span></code> a list is only a special case. In general <code><span class='Value'>π¨</span></code> can be a list of numbers whose length is <code><span class='Value'>π©</span></code>'s rank. So when <code><span class='Function'>=</span><span class='Value'>π©</span></code> is 1, <code><span class='Value'>π¨</span></code> can be length-1 list. For convenience, a number is also allowed, but not an enclosed number (which could be confused with the nested case).</p> +<p>Making <code><span class='Value'>π©</span></code> a list is only a special case. In general <code><span class='Value'>π¨</span></code> can be a list of numbers whose length is <code><span class='Value'>π©</span></code>'s rank. So when <code><span class='Function'>=</span><span class='Value'>π©</span></code> is 1, <code><span class='Value'>π¨</span></code> can be length-1 list. The case above where <code><span class='Value'>π¨</span></code> is a number is a simplification, but an enclosed number <code><span class='Value'>π¨</span></code> isn't allowed because it could be confused with the nested case described below.</p> <a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=4p+oMiww4p+pIOKKkSDihpU04oC/NQ==">βοΈ</a><pre> <span class='Bracket'>β¨</span><span class='Number'>2</span><span class='Separator'>,</span><span class='Number'>0</span><span class='Bracket'>β©</span> <span class='Function'>β</span> <span class='Function'>β</span><span class='Number'>4</span><span class='Ligature'>βΏ</span><span class='Number'>5</span> β¨ 2 0 β© </pre> @@ -40,14 +40,14 @@ <span class='Number'>1</span><span class='Ligature'>βΏ</span><span class='Number'>Β―1</span> <span class='Function'>β</span> <span class='Value'>a</span> 'j' </pre> -<p>This applies even if <code><span class='Value'>π©</span></code> is a unit. By definition it has rank 0, so the only possible value for <code><span class='Value'>π¨</span></code> is the empty list. This extracts an <a href="enclose.html">enclosed</a> element, and returns an atom unchangedβthe atom is promoted to an array by enclosing it, then the action of Pick undoes this. But there's rarely a reason to use this case, because the monadic form First accomplishes the same thing.</p> +<p><code><span class='Value'>π©</span></code> can even be a <a href="enclose.html#whats-a-unit">unit</a>. By definition it has rank 0, so the only possible value for <code><span class='Value'>π¨</span></code> is the empty list. This extracts an <a href="enclose.html">enclosed</a> element, and returns an atom unchangedβthe atom is promoted to an array by enclosing it, then the action of Pick undoes this. But there's rarely a reason to use this case, because the monadic form First accomplishes the same thing.</p> <a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=4p+o4p+pIOKKkSA8J2EnCuKfqOKfqSDiipEgJ2En">βοΈ</a><pre> <span class='Bracket'>β¨β©</span> <span class='Function'>β</span> <span class='Function'><</span><span class='String'>'a'</span> 'a' <span class='Bracket'>β¨β©</span> <span class='Function'>β</span> <span class='String'>'a'</span> 'a' </pre> <h3 id="first"><a class="header" href="#first">First</a></h3> -<p>With no left argument, <code><span class='Function'>β</span></code> is called First, and performs a slight generalization of Pick with a default left argument <code><span class='Number'>0</span><span class='Modifier'>Β¨</span><span class='Function'>β’</span><span class='Value'>π©</span></code>. For a non-empty array it returns the first element in index order.</p> +<p>With no left argument, <code><span class='Function'>β</span></code> is called First, and is the same as Pick with a default left argument <code><span class='Number'>0</span><span class='Modifier'>Β¨</span><span class='Function'>β’</span><span class='Value'>π©</span></code>. For a non-empty array it returns the first element in index order.</p> <a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=4oqRIDwnYScK4oqRICJGaXJzdCIK4oqRIOKGlTTigL8y4oC/NeKAvzE=">βοΈ</a><pre> <span class='Function'>β</span> <span class='Function'><</span><span class='String'>'a'</span> 'a' <span class='Function'>β</span> <span class='String'>"First"</span> @@ -55,9 +55,10 @@ <span class='Function'>β</span> <span class='Function'>β</span><span class='Number'>4</span><span class='Ligature'>βΏ</span><span class='Number'>2</span><span class='Ligature'>βΏ</span><span class='Number'>5</span><span class='Ligature'>βΏ</span><span class='Number'>1</span> β¨ 0 0 0 0 β© </pre> -<p>If <code><span class='Value'>π©</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==">βοΈ</a><pre> <span class='Function'>β</span> <span class='String'>""</span> +<p>And if <code><span class='Value'>π©</span></code> is empty then First results in an error.</p> +<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=4oqRICIiCgriipEg4omiz4A=">βοΈ</a><pre> <span class='Function'>β</span> <span class='String'>""</span> <span class='Error'>Error: β: Argument cannot be empty</span> + <span class='Function'>β</span> <span class='Function'>β’</span><span class='Number'>Ο</span> <span class='Error'>Error: β: Argument cannot be empty</span> </pre> |