[HowTo] LINQ - First Start # Contains Operator

[ppr (Peter Preuss)]

This HowTo introduces the Contains operator

Contains Operator

The Contains Operator from LINQ will check if a particular item is present within a set of items and will return true (when present) or false (when not present).

Overview

I – Input	P – Processing	O – Output
{"A1", "B1", "C1" }	check if “B1” is contained at least 1 time	True
{"AA", "BB", "CC" }	check if “B” is contained at least 1 time	False
{1,2,3,4 }	check if 5 is contained at least 1 time	False

Constraints

For the comparison:

• an existing default equality comparer is used
• The data type of the set elements must be compatible with it

Alternate option:

• Provide a custom equality comparer for the comparison

Implementation

Method Syntax

arrValues | String( ) - a String Array =  new String(){"A1", "B1", "C1" }
hasFound | Boolean = arrValues.Contains("B1") | return: True

Visuals

arrValues | String( ) - a String Array =  new String(){"AA", "BB", "CC" } 	
hasFound | Boolean = arrValues.Contains("B") | return: False

The Contains operator is not to be mixed up with the Contains method of the String class.
The Contains operator checks for the presence of the item in the item set.

Visuals

Query Syntax

The Contains operator is not available as a clause for the query syntax

About equality comparers

An equality comparer implements how two objects (items) are compared for equality.
As shown above, the default equality comparer works successfully and does not need to be explicitly specified. However, for certain data types, it is necessary to pass a specific equality comparer.

Read more about comparers here: [HowTo] LINQ - About # Comparers

Strings / StringComparer

An Equality Comparer specialized for strings is available and can be used e.g. for the case insensitive check.

Datarows / DataRowComparer

If a data table is to be determined to contain a certain data row, this will fail if the default equality comparer is used.

The second row of dt1 and the first row of dt2 can be evaluated as equal because the values of the data row columns are equal: BB,2 = BB,2

Without the use of a specialized equality comparer for data rows, a contains evaluates to false.

For Datarow equality comparisons, the DataRowComparer can be used and offers a default comparison logic.

With the use of the DataRowComparer, a contains evaluates to false

Array / Failing Equality Comparison

In the following, it is demonstrated that the default equality comparer fails e.g. with arrays.

With the out-of-the-box equality comparer, the arrays are not compared on their value basis. Therefore the Contains evaluates to False.

In the .Net world, this case would be addressed with a custom Equality comparer.
In the UiPath world, possible workarounds would be

• List(Of Tuple(Of String, String) as an alternative datatype
  

• A LINQ statement with the Any operator
  

References

[HowTo] LINQ (VB.Net) Learning Catalogue

This topic references the different Learning HowTos related to LINQ. It will be updated on new published HowTos as well LINQ Learning: Topic LINK First Start with LINQ [HowTo] - First Start with LINQ (VB.Net) Exploring the LINQ universe [HowTo] - Exploring the LINQ Universe (VB.Net) Operator [HowTo] Overview Topic LINK Where [HowTo] LINQ - First Start # Where Operator Select work in progress Any [HowTo] LINQ – First Start # Any Operator All [HowTo] LINQ – First Start…

[HowTo] LINQ - About # Comparers

This HowTo introduces the role of Comparers in a LINQ statement Introduction LINQ provides various operators that are used to evaluate the elements in a set of items. The elements are compared with each other for this evaluation. A comparer can be used to influence the comparison. Scenario 1 I – Input P – Processing O – Output {"FR", "IT", "ES" } check if “ES” is contained at least 1 time True {"FR", "IT", "ES" } check if “es” is contained at least 1 time False To do this, the e…

Documentations:

• Enumerable.Contains Methode (System.Linq) | Microsoft Learn
• IEqualityComparer<T> Interface (System.Collections.Generic) | Microsoft Learn
• StringComparer Class (System) | Microsoft Learn
• DataRowComparer<TRow> Class (System.Data) | Microsoft Learn

Questions

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