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ISNULL Function

The ISNULL function tests whether a column of values contains null values. For input column references, this function returns true or false.

  • The NULL function generates null values. See NULL Function.

  • Null values are different from missing values.

Wrangle vs. SQL: This function is part of Wrangle, a proprietary data transformation language. Wrangle is not SQL. For more information, see Wrangle Language.

Basic Usage

isnull(Qty)

Output: Returns true if the value in the Qty column is null.

Syntax and Arguments

isnull(column_string)

Argument

Required?

Data Type

Description

column_string

Y

string

Name of column or string literal to be applied to the function

For more information on syntax standards, see Language Documentation Syntax Notes.

column_string

Name of the column or string literal to be tested for null values.

  • Missing literals or column values generate missing string results.

  • Multiple columns and wildcards are not supported.

Usage Notes:

Required?

Data Type

Example Value

Yes

String literal or column reference

myColumn

Valid data type strings:

When referencing a data type within a transform, you can use the following strings to identify each type:

Note

In Wrangle transforms, these values are case-sensitive.

Note

When specifying a data type by name, you must use the String value listed below. The Data Type value is the display name for the type.

Data Type

String

String

'String'

Integer

'Integer'

Decimal

'Float'

Boolean

'Bool'

Social Security Number

'SSN'

Phone Number

'Phone'

Email Address

'Emailaddress'

Credit Card

'Creditcard'

Gender

'Gender'

Object

'Map'

Array

'Array'

IP Address

'Ipaddress'

URL

'Url'

HTTP Code

'Httpcodes'

Zip Code

'Zipcode'

State

'State'

Date / Time

'Datetime'

Examples

Tip

For additional examples, see Common Tasks.

Example - Type check functions

This example illustrates how various type checking functions can be applied to your data.

Functions:

Item

Description

VALID Function

Tests whether a set of values is valid for a specified data type and is not a null value.

ISMISMATCHED Function

Tests whether a set of values is not valid for a specified data type.

ISMISSING Function

The ISMISSING function tests whether a column of values is missing or null. For input column references, this function returns true or false.

ISNULL Function

The ISNULL function tests whether a column of values contains null values. For input column references, this function returns true or false.

NULL Function

The NULL function generates null values.

Source:

Some source values that should match the State and Integer data types:

State

Qty

CA

10

OR

-10

WA

2.5

ZZ

15

ID

4

Transformation:

Invalid State values: You can test for invalid values for State using the following:

Transformation Name

New formula

Parameter: Formula type

Single row formula

Parameter: Formula

ISMISMATCHED (State, 'State')

The above transform flags rows 4 and 6 as mismatched.

Note

A missing value is not valid for a type, including String type.

Invalid Integer values: You can test for valid matches for Qty using the following:

Transformation Name

New formula

Parameter: Formula type

Single row formula

Parameter: Formula

(ISVALID (Qty, 'Integer') && (Qty > 0))

Parameter: New column name

'valid_Qty'

The above transform flags as valid all rows where theQtycolumn is a valid integer that is greater than zero.

Missing values: The following transform tests for the presence of missing values in either column:

Transformation Name

New formula

Parameter: Formula type

Single row formula

Parameter: Formula

(ISMISSING(State) || ISMISSING(Qty))

Parameter: New column name

'missing_State_Qty'

After re-organizing the columns using the move transform, the dataset should now look like the following:

State

Qty

mismatched_State

valid_Qty

missing_State_Qty

CA

10

false

true

false

OR

-10

false

false

false

WA

2.5

false

false

false

ZZ

15

true

true

false

ID

false

false

true

4

false

true

true

Since the data does not contain null values, the following transform generates null values based on the preceding criteria:

Transformation Name

New formula

Parameter: Formula type

Single row formula

Parameter: Formula

((mismatched_State == 'true') || (valid_Qty == 'false') || (missing_State_Qty == 'true')) ? NULL() : 'ok'

Parameter: New column name

'status'

You can then use the ISNULL check to remove the rows that fail the above test:

Transformation Name

Filter rows

Parameter: Condition

Custom formula

Parameter: Type of formula

Custom single

Parameter: Condition

ISNULL('status')

Parameter: Action

Delete matching rows

Results:

Based on the above tests, the output dataset contains one row:

State

Qty

mismatched_State

valid_Qty

missing_State_Qty

status

CA

10

false

true

false

ok

In this section: