Select filter

From Piki

The select filter is a SQL inspired sample selection tool. You can use it to select samples for removal, or select which samples to keep.

Select
Name	Select
Deployable	Yes
Static	Yes
Sample modifier	Yes
Feature modifier	No

Contents 1 Usage 2 Language 3 Examples 3.1 Selection 3.2 Sorting 4 Settings 5 See also

Usage

The select filter features a SQL resembling query language that is used to to write Boolean expressions. the expression is evaluated for each row and to determine if the row is selected or not. An extra virtual feature 'Row' is added to simplify index based selection.

Language

Operator	Operation
AND	logical and
OR	logical or
<	less then
>	greater then
<=	less or equal to
>=	greater or equal to
<>	not equal to
=	equal to
+	plus
-	minus
*	product
/	division
>=	greater or equal to
%	modulus

Operator	Operation
Sum()	sum
Avg()	average
Min()	minimum
Max()	maximum
Count()	number of rows
StDev()	standard deviation
Var()	variance
IIF(expr, if true, if false)	much like ? : in c

The following characters must be escaped with [] in column names:

~, (, ), #, \, /, =, <, >, +, -, *, %, &, |, ^, ', ", [, ].

Examples

Selection

Operation	Effect
SELECT: " Column1 > Avg(Column3) AND Column5 < 1500 "	Select all samples where Column1 values are larger than the average of column 3 and where Column5 < 1500.
SELECT: " Row % 4 = 0 "	Select every forth row.

Sorting

It is possible to sort the data set in either ascending or descending mode.

Operation	Effect
SORT: " Column3 desc "	Sort samples according to Column3 in descending order.

Settings

The settings can be modified using the settings browser.

Select filter settings
(Operation) Select: Select statement. Sort: Sort statement. (Mode) Mode: Sets the selection mode Keep - Keeps the selected samples. Remove - Removes the selected samples. Training: If the filter should be applied to the training set. Validation: If the filter should be applied to the validation set.

See also

• Filter - Article covering general filter principles.
• List of Filter components - List of all available filters.
• Data unit - Article explaining data units in detail.
• Data - Article explaining essential data concepts.