How to build a histogram for a list of int in C# [duplicate]

Answer 1

 int highestAppearanceNum = demoList.GroupBy(i => i)
            .OrderByDescending(grp => grp.Count())
            .Select(grp => grp.First())
            .First();

Edit: If you also want to know which number appears how often:

var appearances = demoList.GroupBy(i => i)
    .OrderByDescending(grp => grp.Count())
    .Select(grp => new { Num = grp.Key, Count = grp.Count() });
if (appearances.Any())
{
    int highestAppearanceNum = appearances.First().Num;     // 1
    int highestAppearanceCount = appearances.First().Count; // 5
}