# 4.1 Local Neighbor Match Test

The local neighbor match test ([2020](https://geodacenter.github.io/workbook/6c_local_multi/lab6c.html#ref-AnselinLi:20)) is a method to identify significant locations by assessing the extent of overlap between k-nearest neighbors in geographical space and k-nearest neighbors in multi-attribute space. For more information, please read <https://geodacenter.github.io/workbook/6c_local_multi/lab6c.html#local-neighbor-match-test>

## neighbor\_match\_test()

{% hint style="info" %}
neighbor\_*match\_test*() is a PostgreSQL WINDOW function. Please call it  with an OVER clause.
{% endhint %}

### Synopsis

Short version:

```sql
float[] neighbor_match_test(geometry the_geom, anyarray vals, integer k)
```

Long version:

```sql
float[] neighbor_match_test(geometry the_geom, anyarray vals, integer k,
    character varying scale_method,
    character varying distance_method
)
```

Full version:

```sql
float[] neighbor_match_test(geometry the_geom, anyarray vals, integer k,
    character varying scale_method,
    character varying distance_method
    float power, 
    boolean is_inverse, 
    boolean is_arc
    boolean is_mile
)
```

### Arguments

| Name             | Type              | Description                                                                                                                                          |
| ---------------- | ----------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------- |
| the\_geom        | geometry          | the geometry column (only points and polygons are supported)                                                                                         |
| vals             | *anyarray*        | an array of numeric columns that contains the values for neighbor match test                                                                         |
| k                | integer           | k nearest neighbor for both attribute and geographical space                                                                                         |
| scale\_method    | character varying | the scaling method. Options are {'*raw*', '*standardize*', '*demean*', '*mad*', '*range\_standardize*', '*range\_adjust*'}. Default: '*standardize*' |
| distance\_method | character varying | the distance method. Options are {'*euclidean*', '*manhattan*'. Default: '*euclidean*'.                                                              |
| power            | float             | the power/exponent corresponds to the number of times the base (dist\_band) is used as a factor. Default: 1.                                         |
| is\_inverse      | boolean           | if apply inverse on distance value. Default: False.                                                                                                  |
| is\_arc          | boolean           | if compute arc distance between two observations. Default: FALSE.                                                                                    |
| is\_mile         | boolean           | if convert distance unit from mile to kilometer(KM). Default: TRUE.                                                                                  |

### Return

| Type     | Description                                                              |
| -------- | ------------------------------------------------------------------------ |
| float\[] | an array contains 2 values, which are {'*cardinality*', '*probability*'} |

{% hint style="info" %}
**cardinality**: the number of common neighbors for each location
{% endhint %}

### Examples

Apply local neighbor match test on 6 nearest neighbors of the variables \["hr60", "ue60"] (homicide and unemployment rate 1960 in [natregimes dataset](https://geodacenter.github.io/data-and-lab/natregimes/)):

{% hint style="info" %}
Please see chapter '[Contiguity Based Weights](/postgeoda/2.-spatial-weights/2.1-contiguity-based-weights.md)' for how to create a Queen contiguity weights.
{% endhint %}

```sql
SELECT neighbor_match_test(the_geom, ARRAY[hr60, ue60], 6) OVER() FROM natregimes;

   neighbor_match_test    
--------------------------
 {0,-1}
 {0,-1}
 {0,-1}
 {0,-1}
 {0,-1}
 {0,-1}
 {0,-1}
 {0,-1}
 {0,-1}
 {0,-1}
 {0,-1}
 {0,-1}
 {1,0.0115787398060671}
 {1,0.0115787398060671}
 ...
```

###


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