mongodb: finding the highest numeric value of a column - php

Question

I have MongoDB collection of documents containing several fields. One of the columns/fields should be numeric only, but some of these fields contain non-numerical (corrupt) data as string values. I should find the highest numerical value of this column, excluding the corrupt, non-numerical data. I am aware of the question Getting the highest value of a column in MongoDB, but AFAIK, this extended case was not covered.
The example below depicts the issue. For the highest value, the document with "age": 70 should be returned:
[
{
"id": "aa001",
"age": "90"
},
{
"id": "bb002",
"age": 70
},
{
"id": "cc003",
"age": 20,
}
]
Providing a PHP example for the find() / findOne() query would be of much help. Thanks a lot!
JohnnyHK came up with the perfect solution. Here's the working PHP code:
$cursor = $collection->find(array('age' => array('$not' => array('$type' => 2))), array('age' => 1));
$cursor->sort(array('age' => -1))->limit(1);

Answer 1

You can use the $type operator with $not in your query to exclude docs where age is a string. In the shell your query would look like:
db.test.find({age: {$not: {$type: 2}}}).sort({age: -1}).limit(1)
Or in PHP from Martti:
$cursor = $collection->find(array('age' => array('$not' => array('$type' => 2))), array('age' => 1));
$cursor->sort(array('price' => -1))->limit(1);

Answer 2

with PHP driver (mongodb)
using findOne()
$filter=[];
$options = ['sort' => ['age' => -1]]; // -1 is for DESC
$result = $collection->findOne(filter, $options);
$maxAge = $result['age']

Answer 3

You can use aggregate function to get maximum number from collections like this.
$data=$collection->aggregate(array
( '$group'=>
array('_id'=>'',
'age'=>array('$max'=>'$age'.)
)
)
);

Answer 4

This works for me
$options = ['limit' => 100,'skip' => 0, 'projection' => ['score' => ['$meta' => 'textScore']], 'sort' => ['score' => ['$meta' => 'textScore']]];