# Transform vs copy\_to, text concatenation used for aggregation

**URL:** <https://discuss.elastic.co/t/transform-vs-copy-to-text-concatenation-used-for-aggregation/31781>\
**Category:** Elasticsearch\
**Created:** [October 7, 2015, 2:45pm UTC](https://discuss.elastic.co/t/transform-vs-copy-to-text-concatenation-used-for-aggregation/31781 "2015-10-07T14:45:53Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![noelyim](https://avatars.discourse-cdn.com/v4/letter/n/8491ac/32.png) [@noelyim](https://discuss.elastic.co/u/noelyim)\
**Post date:** [October 7, 2015, 2:45pm UTC](https://discuss.elastic.co/t/transform-vs-copy-to-text-concatenation-used-for-aggregation/31781/1 "2015-10-07T14:45:54Z")

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I have similar question as this poster:

I have 2 fields:

1. doc\_a.prop.proptexta
2. doc\_a.prop.proptextb

I want to identify if there are duplication using this 2 fields of doc\_a. So, i tried

copyto:  
I create a mapping and in both proptexta and proptextb put copy\_to proptextab, and using the new field proptextab  
I assumed proptextab would be a concatenation of proptexta and proptextb, then, I did a aggregation on proptextab and the result buckets are separated:

say. proptexta = 123, proptextb= abc

in my aggregation result using proptextab.  
I have

```
buckets: 
key: "123" 
doc_count:...
key: "abc"
doc_count:....

```

Which I was expecting

```
buckets:
key: 123abc
doc_count:...

```

So now.. I'm researching transform script in mapping...I am not sure it will work neither.

Continuing the discussion from [Is it possible to use transform scripts in mappings to alter document \_id?](https://discuss.elastic.co/t/is-it-possible-to-use-transform-scripts-in-mappings-to-alter-document--id/20984):

> [@Is it possible to use transform scripts in mappings to alter document \_id?](https://discuss.elastic.co/t/is-it-possible-to-use-transform-scripts-in-mappings-to-alter-document--id/20984/1):
>
> The Elasticsearch documentation is always frustratingly silent on the  
> things I seem to need to accomplish to make life easier.
> 
> Is it possible to use a transform script in a mapping to alter the document  
> \_id? This would be a convenient way to de-dup incoming data I have too  
> little control over if so.
> 
> After digging around online and not finding much of use, I naively tried  
> this in Elasticsearch 1.4, which alas did nothing:
> 
> "typename": {  
> "transform": {  
> "script": "ctx.\_source['useAsId'] = ctx.\_source['a'] + ctx.\_source['b']"  
> ,  
> "lang": "groovy"  
> },  
> "\_id" {  
> "path": "useAsId"  
> },  
> "properties": {  
> "a": { "type": "string" },  
> "b": { "type": "string" },  
> "useAsId": { "type": "string" }  
> }  
> }
> 
> It seems that the ordering of operations isn't what I'd like it to be under  
> the hood; I don't get the \_id I'd want out of this, but rather get the  
> standard auto-assigned \_id value.
> 
> So is there a way to process an incoming document to alter the \_id value in  
> this sort of way? Or there another more generally accepted route to  
> de-duping?
> 
> --  
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---

<div class="post-metadata">

**Author:** ![nik9000](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/nik9000/32/44947_2.png) [@nik9000](https://discuss.elastic.co/u/nik9000)\
**Post date:** [October 7, 2015, 3:05pm UTC](https://discuss.elastic.co/t/transform-vs-copy-to-text-concatenation-used-for-aggregation/31781/2 "2015-10-07T15:05:55Z")

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`copy_to` makes a multi-valued field rather than one who's value is the concatenation of the two values. Its

```auto
{
  "key": ["123", "abc"]
}

```

rather than

```auto
{
  "key": "123abc"
}

```

Transform _could_ be used to make what you are looking for but I advise against it because its deprecated/dangerously difficult to debug. Your best bet is to do the concatenation in your application on the way into elasticsearch. That way you can get the \_source back to verify that it worked properly.

---

<div class="post-metadata">

**Author:** ![noelyim](https://avatars.discourse-cdn.com/v4/letter/n/8491ac/32.png) [@noelyim](https://discuss.elastic.co/u/noelyim)\
**Post date:** [October 7, 2015, 3:16pm UTC](https://discuss.elastic.co/t/transform-vs-copy-to-text-concatenation-used-for-aggregation/31781/3 "2015-10-07T15:16:49Z")

</div>

Thank you for the quick reply.

I also wonder if I can use script for the fields in aggregation.  
I am able to do this with my two set of docs( doc\_a and doc\_b) in one index, works fine with one field proptexta:

```
"aggs"
    "MyAggResultComparingTwoDocNames": {
       "terms" : {
            "script": "doc[doc_a.prop.proptexta].values + doc[doc_b.prop.proptexta].values"

```

Is there a groovy script solution for the following?

```
(concatentate(doc_a.prop.proptexta,doc_a.prop.proptextb)).values + (concatentate(doc_b.prop.proptexta,doc_b.prop.proptextb)).values
```

---

<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:** [July 5, 2017, 11:46pm UTC](https://discuss.elastic.co/t/transform-vs-copy-to-text-concatenation-used-for-aggregation/31781/4 "2017-07-05T23:46:07Z")

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