Check out example codes for ".netstandard distinctby iqueryable". It will help you in understanding the concepts better.

Code Example 1

public static IQueryable<TSource> DistinctBy<TSource, TKey>(
	this IQueryable<TSource> source,
    Expression<Func<TSource, TKey>> keySelector)
    {
    	return source.GroupBy(keySelector).Select(grouping => grouping.FirstOrDefault());
	}

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