crankshaft/doc/11_kmeans.md

K-Means Functions

CDB_KMeans(subquery text, no_clusters integer)

This function attempts to find n clusters within the input data. It will return a table to CartoDB ids and the number of the cluster each point in the input was assigend to.

Arguments

Name	Type	Description
subquery	TEXT	SQL query that exposes the data to be analyzed (e.g., SELECT * FROM interesting_table). This query must have the geometry column name the_geom and id column name cartodb_id unless otherwise specified in the input arguments
no_clusters	INTEGER	The number of clusters to try and find

Returns

A table with the following columns.

Column Name	Type	Description
cartodb_id	INTEGER	The CartoDB id of the row in the input table.
cluster_no	INTEGER	The cluster that this point belongs to.

Example Usage

SELECT
    customers.*,
    km.cluster_no
FROM
   cdb_crankshaft.CDB_Kmeans('SELECT * from customers' , 6) km, customers_3
WHERE
    customers.cartodb_id = km.cartodb_id

CDB_WeightedMean(subquery text, weight_column text, category_column text)

Function that computes the weighted centroid of a number of clusters by some weight column.

Arguments

Name	Type	Description
subquery	TEXT	SQL query that exposes the data to be analyzed (e.g., SELECT * FROM interesting_table). This query must have the geometry column and the columns specified as the weight and category columns
weight_column	TEXT	The name of the column to use as a weight
category_column	TEXT	The name of the column to use as a category

Returns

A table with the following columns.

Column Name	Type	Description
the_geom	GEOMETRY	A point for the weighted cluster center
class	INTEGER	The cluster class

Example Usage

SELECT
    ST_Transform(m.the_geom, 3857) AS the_geom_webmercator,
    m.class
FROM
    cdb_crankshaft.cdb_WeightedMean(
        'SELECT * FROM customers',
        'customer_value',
        'cluster_no') AS m