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BottomCount (DMX)

Returns the specified number of bottom-most rows, in increasing order of rank as specified by an expression.


BottomCount(<table expression>, <rank expression>, <count>)

An expression that returns a table, such as a <table column reference>, or a function that returns a table.

<table expression>

The value that is supplied by the <rank expression> argument determines the increasing order of rank for the rows that are supplied in the <table expression> argument, and the number of bottom-most rows that is specified in the <count> argument is returned.

The following example creates a prediction query against the Association model that you build by using the Basic Data Mining Tutorial.

To understand how BottomCount works, it might be helpful to first execute a prediction query that returns only the nested table.

SELECT Predict ([Association].[v Assoc Seq Line Items], INCLUDE_STATISTICS, 10)
FROM 
     [Association]
NATURAL PREDICTION JOIN
SELECT (SELECT 'Women''s Mountain Shorts' as [Model]) AS [v Assoc Seq Line Items]) AS t
NoteNote

In this example, the value supplied as input contains a single quotation mark, and therefore must be escaped by prefacing it with another single quotation mark. If you are not sure of the syntax for inserting an escape character, you can use the Prediction Query Builder to create the query. When you select the value from the dropdown list, the required escape character is inserted for you. For more information, see How to: Create a Singleton Query in the Data Mining Designer.

Example results:

Model

$SUPPORT

$PROBABILITY

$ADJUSTEDPROBABILITY

Sport-100

4334

0.291283016

0.252695851

Water Bottle

2866

0.192620472

0.175205052

Patch kit

2113

0.142012232

0.132389356

Mountain Tire Tube

1992

0.133879965

0.125304948

Mountain-200

1755

0.117951475

0.111260823

Road Tire Tube

1588

0.106727603

0.101229538

Cycling Cap

1473

0.098998589

0.094256014

Fender Set - Mountain

1415

0.095100477

0.090718432

Mountain Bottle Cage

1367

0.091874454

0.087780332

Road Bottle Cage

1195

0.080314537

0.077173962

The BottomCount function takes the results of this query and returns the smallest-valued rows that sum to the specified percentage.

SELECT 
BottomCount
    (
    Predict ([Association].[v Assoc Seq Line Items],INCLUDE_STATISTICS,10),
    $SUPPORT,
    3)
FROM 
     [Association]
NATURAL PREDICTION JOIN
(SELECT (SELECT 'Women''s Mountain Shorts' as [Model]) AS [v Assoc Seq Line Items]) AS t

The first argument to the BottomCount function is the name of a table column. In this example, the nested table is returned by calling the Predict function and using the INCLUDE_STATISTICS argument.

The second argument to the BottomCount function is the column in the nested table that you use to order the results. In this example, the INCLUDE_STATISTICS option returns the columns $SUPPORT, $PROBABILTY, and $ADJUSTED PROBABILITY. This example uses $SUPPORT because support values are not fractional and therefore are easier to verify.

The third argument to the BottomCount function specifies the number of rows. To get the three lowest-ranked rows, as ordered by $SUPPORT, you type 3.

Example results:

Model

$SUPPORT

$PROBABILITY

$ADJUSTEDPROBABILITY

Road Bottle Cage

1195

0.080314537

0.077173962

Mountain Bottle Cage

1367

0.091874454

0.087780332

Fender Set - Mountain

1415

0.095100477

0.090718432

Note   This example is provided only to illustrate the use of BottomCount. Depending on the size of your data set, this query might take a long time to run.

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