blocks|key|4028784|text|您可以使用.map()和.slice()方法：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4028785|​|4028786|var+my_array+=+[[0,1,2],
++++++++++++++++[3,4,5],
++++++++++++++++[6,7,8]];
++++++++++++++++
var+result+=+my_array.slice(0,+2).map(a+=>+a.slice(0,+2));

console.log(result);|code-block|syntax|javascript|4028787|.as-console-wrapper+{+max-height:+100%25+!important;+top:+0;+}|4028788|4028789|entityMap^0|5|6|C|8|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|X|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|O|3|G|5|6|7|Z|8|@]|D|@]|E|$]]|$1|P|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|Q|$]]

<p>You can use <code>.map()</code> and <code>.slice()</code> methods:</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>var my_array = [[0,1,2],
                [3,4,5],
                [6,7,8]];
                
var result = my_array.slice(0, 2).map(a =&gt; a.slice(0, 2));

console.log(result);</code></pre>
<pre class="snippet-code-css lang-css prettyprint-override"><code>.as-console-wrapper { max-height: 100% !important; top: 0; }</code></pre>
</div>
</div>
</p>


blocks|key|4028831|text|可以使用Array.slice和Array.map的组合|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4028832|​|4028833|const+input+=+[
++[0,+1,+2],
++[3,+4,+5],
++[6,+7,+8]
];

const+result+=+input.slice(0,+2).map(arr+=>+arr.slice(0,+2));

console.log(result);|code-block|syntax|javascript|4028834|4028835|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice|1|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map^0|4|B|G|9|4|B|0|G|9|1|0|0|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]]|D|@$9|12|A|13|1|14]|$9|15|A|16|1|17]]|E|$]]|$1|F|3|G|5|6|7|18|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|19|8|@]|D|@]|E|$K|L]]|$1|M|3|G|5|6|7|1A|8|@]|D|@]|E|$]]|$1|N|3|-4|5|6|7|1B|8|@]|D|@]|E|$]]]|O|$P|$5|Q|R|S|E|$T|U]]|V|$5|Q|R|S|E|$T|W]]]]

<p>Could use a combination of <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice" rel="nofollow noreferrer"><code>Array.slice</code></a> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map" rel="nofollow noreferrer"><code>Array.map</code></a>:</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const input = [
  [0, 1, 2],
  [3, 4, 5],
  [6, 7, 8]
];

const result = input.slice(0, 2).map(arr =&gt; arr.slice(0, 2));

console.log(result);</code></pre>
</div>
</div>
</p>


blocks|key|4028880|text|它看起来不像是一个3x#数组，它只是一个数组的数组。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4028881|您可以首先使用slice来获取仅包含前两个元素的数组，即|4028882|[[0,+1,+2],[3,+4,+5]]|code-block|syntax|javascript|4028883|然后使用reduce返回一个新数组&在该数组中只获取前两个值|4028884|​|4028885|var+my_array+=+[
++[0,+1,+2],
++[3,+4,+5],
++[6,+7,+8]
];

let+x+=+my_array.slice(0,+2).reduce(function(acc,+curr)+{
++acc.push(curr.slice(0,+2))
++return+acc;
},+[])
console.log(x)|4028886|4028887|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|T|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|U|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|V|8|@]|9|@]|A|$]]|$1|M|3|N|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|O|3|L|5|6|7|X|8|@]|9|@]|A|$]]|$1|P|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|Q|$]]

<p>It dont seems to a 3x# array , it is just array of arrays.</p>

<p>You can first use slice to get an array of only first two elements that is  </p>

<pre><code>[[0, 1, 2],[3, 4, 5]]
</code></pre>

<p>then use reduce to return a new array &amp; inside it get only the first two values</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>var my_array = [
  [0, 1, 2],
  [3, 4, 5],
  [6, 7, 8]
];

let x = my_array.slice(0, 2).reduce(function(acc, curr) {
  acc.push(curr.slice(0, 2))
  return acc;
}, [])
console.log(x)</code></pre>
</div>
</div>
</p>


blocks|key|4028918|text|您可以将对象作为索引和所需的子数组的长度。然后切片并映射切片的子数组。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4028919|​|4028920|var+array+=+[[0,+1,+2],+[3,+4,+5],+[6,+7,+8]],
++++length+=+{+x:+2,+y:+2+},
++++indices+=+{+i:+0,+j:+0+},
++++result+=+array.slice(indices.i,+indices.i+%2B+length.x).map(a+=>+a.slice(indices.j,+indices.j+%2B+length.y));
++++
console.log(result);|code-block|syntax|javascript|4028921|4028922|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$G|H]]|$1|I|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|P|8|@]|9|@]|A|$]]]|K|$]]

<p>You could take objects for the indices and for the length of the wanted sub arrays.. Then slice and map the sliced sub arrays.</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>var array = [[0, 1, 2], [3, 4, 5], [6, 7, 8]],
    length = { x: 2, y: 2 },
    indices = { i: 0, j: 0 },
    result = array.slice(indices.i, indices.i + length.x).map(a =&gt; a.slice(indices.j, indices.j + length.y));
    
console.log(result);</code></pre>
</div>
</div>
</p>


blocks|key|4030304|text|​|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4030305|const+input+=+[
++[0,+1,+2],
++[3,+4,+5],
++[6,+7,+8]
];
let+result+=[]
input.forEach(([a,+b],+index)+=>+{if(index+<+2)+result.push([a,+b])})

console.log(result);|code-block|syntax|javascript|4030306|4030307|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|K|8|@]|9|@]|A|$E|F]]|$1|G|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|M|8|@]|9|@]|A|$]]]|I|$]]

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const input = [
  [0, 1, 2],
  [3, 4, 5],
  [6, 7, 8]
];
let result =[]
input.forEach(([a, b], index) =&gt; {if(index &lt; 2) result.push([a, b])})

console.log(result);</code></pre>
</div>
</div>
</p>


blocks|key|4028989|text|如果您打算大量使用矩阵，那么您应该查看math.js。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4028990|尝试以下操作：|4028991|var+my_array+=+[[0,1,2],
++++++++++++++++[3,4,5],
++++++++++++++++[6,7,8]];

var+matrix+=+math.matrix(my_array);

var+subset+=+matrix.subset(math.index([0,+1],+[0,+1]));|code-block|syntax|javascript|4028992|工作example。|4028993|entityMap|0|LINK|mutability|MUTABLE|url|http://mathjs.org/docs/datatypes/matrices.html|1|https://codepen.io/anon/pen/pxEJLJ^0|J|7|0|0|0|0|2|7|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|6|7|10|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|11|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|12|8|@]|9|@$A|13|B|14|1|15]]|C|$]]|$1|M|3|-4|5|6|7|16|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]]]

<p>If you are going to work a lot with matrices, then you should check out <a href="http://mathjs.org/docs/datatypes/matrices.html" rel="nofollow noreferrer">math.js</a>.  </p>

<p>Try the following:</p>

<pre><code>var my_array = [[0,1,2],
                [3,4,5],
                [6,7,8]];

var matrix = math.matrix(my_array);

var subset = matrix.subset(math.index([0, 1], [0, 1]));
</code></pre>

<p>Working <a href="https://codepen.io/anon/pen/pxEJLJ" rel="nofollow noreferrer">example</a>.</p>


<p>I have a 3x3 array:</p>

<pre><code>var my_array = [[0,1,2],
                [3,4,5],
                [6,7,8]];
</code></pre>

<p>and want to get the first 2x2 block of it (or any other 2x2 block):</p>

<pre><code>[[0,1], 
 [3,4]]
</code></pre>

<p>with numpy I would have written:</p>

<pre><code>my_array = np.arange(9).reshape((3,3))
my_array[:2, :2]
</code></pre>

<p>to get the correct result.</p>

<p>I tried in javascript:</p>

<pre><code>my_array.slice(0, 2).slice(0, 2);
</code></pre>

<p>but the second slice affects the first dimension, doing nothing.
Am I doomed to use for loop or is there some new ES6 syntax that would make my life simpler?</p>


array index selection like in numpy but in javascript

我有一个3x3数组：var my_array = [[0,1,2],                [3,4,5],                [6,7,8]];并希望获得它的第一个2x2块(或任何其他2x2块)：[[0,1],  [3,4]]对于numpy，我会写道：my_array = np.arange(9)...

问与numpy中的数组索引选择类似，但在javascript中
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问与numpy中的数组索引选择类似，但在javascript中
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