How to Count String Values with LINQ in VB.NET

Описание: Learn how to use LINQ in VB.NET to count occurrences of string values in a list while maintaining their order.
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This video is based on the question https://stackoverflow.com/q/65728424/ asked by the user 'George' ( https://stackoverflow.com/u/1655087/ ) and on the answer https://stackoverflow.com/a/65729918/ provided by the user 'Jimi' ( https://stackoverflow.com/u/7444103/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Count String Values with LINQ in VB.NET

When dealing with a list of values in a string format, especially if they are delimited (like by pipes |), counting the occurrences of each unique value while maintaining the original order can be a bit tricky. This guide will help you understand how to achieve that using LINQ in VB.NET.

Understanding the Problem

Imagine you have a string of account identifiers, separated by pipes. For instance:

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You need to create a new list that counts how many times each identifier appears but retains the sequence of the original list. The expected output for the above input would be:

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This means that:

The account 111 appears 4 times

The account 222 appears 1 time

The account 333 appears 3 times

The account 444 appears 1 time

The account 555 appears 2 times

Step-by-Step Solution

1. Splitting the Input String

The first step is to split the input string into an array to handle each identifier separately.

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2. Grouping by Identifier

Next, we group the split values by their identifiers. This allows us to count how many times each identifier appears.

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3. Generating the Output

Now, we will create the output string by referencing the original split values but using the counts from our dictionary of groups.
There are two primary ways you can generate the output string: using Aggregate() with a StringBuilder or simply joining the values directly.

Method A: Using StringBuilder (for Segmented or Complex Situations)

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Method B: Using Join (a Simpler Approach)

This method is more straightforward and utilizes the String.Join() method:

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Complete Example Code

Here’s the complete code snippet that combines everything together:

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Conclusion

With the methods outlined above, you can effectively count the occurrences of string values in a delimited list using LINQ in VB.NET while preserving the order of the input. Whether you need a complex aggregation or a simple string join, LINQ provides the flexibility to achieve your desired output easily.

Feel free to adapt this code to fit into your own applications and handle your unique requirements!