<p>Hi ,
I have an issue with the Datastore when im trying to do batch operations.
I want to protect the 500 entities per batch limit.</p>
<p>What is the best way to split the slice to 500 entities per slice ?
let </p>
<p><a href="https://github.com/golang/go/wiki/SliceTricks">SliceTricks</a>
Maybe curing the slice to a new one like that ?
a = append(a[:i], a[j:]...)</p>
<p>Im basically want to tack a slice of size N and split it to 500 each</p>
<hr/>**评论：**<br/><br/>ergotayours: <pre><p>Can you be more specific? I'm not sure I understand what you're trying to accomplish.</p>
<p>Are you trying to split the slice into sections of 500 each? If so, you could do something like</p>
<pre><code>for i := 0; i < len(a); i += 500 {
batch := a[i:min(i+500, len(a))]
// Do something with batch
}
</code></pre>
<p>where <code>min</code> would be something like</p>
<pre><code>func min(a, b int) int {
if a <= b {
return a
}
return b
}
</code></pre>
<p>The last <code>batch</code> might contain less than 500 elements, which sounds like it's okay given your description.</p>
<p>EDIT: As <a href="/u/miko5054">/u/miko5054</a> points out, the upper slice bound is exclusive, so it should be <code>min(i+500, len(a))</code>. Sorry for the error; I haven't done slice stuff in a while!</p></pre>miko5054: <pre><blockquote>
<p>func min(a, b int) int {
if a <= b {
return a
}
return b
}</p>
</blockquote>
<p>i think this is the correct way ?</p>
<pre><code> a := []int{1, 2, 3, 4, 5, 6, 7, 8}
for i := 0; i < len(a); i += 2 {
batch := a[i:min(i+2, len(a))] <----
fmt.Println(batch)
}
</code></pre></pre>SteveMcQwark: <pre><p>Yes, you want to slice to <code>len(a)</code> because it's an exclusive bound, and you want to include the last element at <code>len(a)-1</code>. <code>i + stride</code> should already give you the element <em>after</em> the batch, so that's fine.</p></pre>mc_hammerd: <pre><p>slicetricks says <code>b = append(a[:500], a[500:]...)</code></p>
<p>my guess would be skipping the append is faster</p>
<p>(slices are just pointers to arrays so this should be fast).</p>
<pre><code>lena := len(a)
lenb := lena/500+1
b := make([][]int,lenb) // for example ill use int
for i,_ := range b {
start := i*500
end := start+500
if end > lena { end=lena }
b[i] = a[start:end]
}
for i,v := range b { fmt.Println(i,":",v) } //print
</code></pre></pre>barsonme: <pre><p>I'd benchmark it. I have a feeling append won't be the fastest, but don't listen to me -- benchmark.</p>
<p>The non-append way would be to allocate len(slice)/500 and then copy over in chunks. </p></pre>
