# Obtain last 2 elements of nested object and perform logic on them

**URL:** <https://discuss.elastic.co/t/obtain-last-2-elements-of-nested-object-and-perform-logic-on-them/193177>\
**Category:** Elasticsearch\
**Created:** [July 31, 2019, 4:22pm UTC](https://discuss.elastic.co/t/obtain-last-2-elements-of-nested-object-and-perform-logic-on-them/193177 "2019-07-31T16:22:26Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![hv09](https://avatars.discourse-cdn.com/v4/letter/h/59ef9b/32.png) [@hv09](https://discuss.elastic.co/u/hv09)\
**Post date:** [July 31, 2019, 4:22pm UTC](https://discuss.elastic.co/t/obtain-last-2-elements-of-nested-object-and-perform-logic-on-them/193177/1 "2019-07-31T16:22:27Z")

</div>

Hello all,

I've been reading ES docs, SO and this forums' posts about this for the past 2 days, but I can't seem to figure it out.

Given this data structure, which is a part of a bigger data structure that represents a user:

```auto
"reviews": [
            {
              "userEmail": "user1@email.com",
              "time": "2019-07-31T00:28:21.988315333Z",
              "userName": "User 1",
              "user": "1",
              "fieldIWantToCompare": 1
            },
            {
              "userEmail": "user2@email.com",
              "time": "2019-07-31T00:28:21.988315333Z",
              "userName": "User 2",
              "user": "2",
              "fieldIWantToCompare": 0
            },
            {
              "userEmail": "user3@email.com",
              "time": "2019-07-31T00:28:21.988315333Z",
              "userName": "User 3",
              "user": "3",
              "fieldIWantToCompare": 1
            }
            ...
          ]

```

`reviews` is a nested object.

How can I (if even possible at all) select the last 2 elements of this nested object to then perform some logic on their fields? What I want to do is compare a field on the last object and the penultimate object, and if they're not the same AND match a parameter, I want the query to filter the whole bigger structure in.

Here's a snippet of (Go) code that outlines what I'd do to get what I want on a normal application.  
This is essentially what I want to do in ES:

```auto
previous := reviews[len(reviews) - 2]
current := reviews[len(reviews) - 1]

if previous.fieldIWantToCompare == <some_parameter_here> && previous.fieldIWantToCompare != current.fieldIWantToCompare {
    return true // The whole user would be returned by the query.
}

```

I've tried using scripts to get the length of fields but I can't seem to make it work as this is a nested object and I don't think I fully understand how they work.  
I know they're flattened by ES like so:

```auto
{
"reviews.userEmail" : ["user1@email.com", "user2@email.com", "user3@email.com"],
"reviews.userName": ["User 1", "User 2", "User 3"]
...
}

```

But I don't understand how to access the lengths of these arrays or how to access their data, essentially by array index.

Thanks!

---

<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:** [August 28, 2019, 4:22pm UTC](https://discuss.elastic.co/t/obtain-last-2-elements-of-nested-object-and-perform-logic-on-them/193177/2 "2019-08-28T16:22:27Z")

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