# Sorting in painless

**URL:** <https://discuss.elastic.co/t/sorting-in-painless/87174>\
**Category:** Elasticsearch\
**Created:** [May 25, 2017, 7:29pm UTC](https://discuss.elastic.co/t/sorting-in-painless/87174 "2017-05-25T19:29:35Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Nick\_Peterson](https://avatars.discourse-cdn.com/v4/letter/n/ea5d25/32.png) [@Nick\_Peterson](https://discuss.elastic.co/u/Nick_Peterson)\
**Post date:** [May 25, 2017, 7:29pm UTC](https://discuss.elastic.co/t/sorting-in-painless/87174/1 "2017-05-25T19:29:35Z")

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Hi,

I had the following line in a groovy script that I'm attempting to rewrite into painless -

```
def buckets = ctx.payload.aggregations.metrics.buckets.sort(a,b -> a.largest_surprise.value == b.largest_surprise.value ? 0 : a.largest_surprise.value < b.largest_surprise.value ? -1 : 1);

```

The compile error I'm getting is "Variable [a] is not defined."

It looks like painless supports the Collections.sort method in java so I tried -

```
Collections.sort(ctx.payload.aggregations.metrics.buckets, a,b -> a.largest_surprise.value == b.largest_surprise.value ? 0 : a.largest_surprise.value < b.largest_surprise.value ? -1 : 1);

```

But that also has a compile error - "Unknown call [sort] with [3] arguments on type [Collections]."

Is it possible to sort in painless with a lambda? If so, then what is the syntax? Also, are there any better references for painless than [https://www.elastic.co/guide/en/elasticsearch/painless/master/painless-api-reference.html](https://www.elastic.co/guide/en/elasticsearch/painless/master/painless-api-reference.html)?

Thanks,  
Nick

---

<div class="post-metadata">

**Author:** ![Nick\_Peterson](https://avatars.discourse-cdn.com/v4/letter/n/ea5d25/32.png) [@Nick\_Peterson](https://discuss.elastic.co/u/Nick_Peterson)\
**Post date:** [May 25, 2017, 8:54pm UTC](https://discuss.elastic.co/t/sorting-in-painless/87174/2 "2017-05-25T20:54:03Z")

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Found a page describing lambdas in painless - [https://www.elastic.co/guide/en/elasticsearch/reference/5.4/modules-scripting-painless-syntax.html#painless-lambda-expressions](https://www.elastic.co/guide/en/elasticsearch/reference/5.4/modules-scripting-painless-syntax.html#painless-lambda-expressions).

I think I was missing enclosing parantheses around "a,b" as

```
def buckets = ctx.payload.aggregations.metrics.buckets.sort((a,b) -> a.largest_surprise.value == b.largest_surprise.value ? 0 : a.largest_surprise.value < b.largest_surprise.value ? -1 : 1);

```

compiles.

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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [June 22, 2017, 8:54pm UTC](https://discuss.elastic.co/t/sorting-in-painless/87174/3 "2017-06-22T20:54:05Z")

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