c# Find all common substring in List<string>

Question

How can I extract all words, which are common in a list of strings?

Example:

//Output = Bammler GOV
  "Bammler Tokyo SA GOV"
  "Zurich Bammler GOV"
  "London Bammler 12 GOV"
  "New Bammler York GOV"

I tried following:

    static void Main(string[] args)
    {
        List<string> MyStringList = new List<string>()
        {
            "Bammler Tokyo SA GOV",
            "Zurich Bammler GOV",
            "London Bammler 12 GOV",
            "New Bammler York GOV"
        };

        string shortest = MyStringList.OrderBy(s => s.Length).First();
        IEnumerable<string> shortestSubstrings = getAllSubstrings(shortest).OrderByDescending(s => s.Length);
        var other = MyStringList.Where(s => s != shortest).ToArray();
        string longestCommonIntersection = string.Empty;
        foreach (string subStr in shortestSubstrings)
        {
            bool allContains = other.All(s => s.Contains(subStr));
            if (allContains)
            {
                longestCommonIntersection = subStr;
                break;
            }
        }
    }

    public static IEnumerable<string> getAllSubstrings(string word)
    {
        return from charIndex1 in Enumerable.Range(0, word.Length)
               from charIndex2 in Enumerable.Range(0, word.Length - charIndex1 + 1)
               where charIndex2 >= 2
               select word.Substring(charIndex1, charIndex2);
    }

I found this here Find a common string within a list of strings but this will just extract for example "Bammler".

What have you tried? You can't expect us to do all the work for you... — maccettura
– maccettura, Commented Jul 18, 2017 at 15:00
StackOverflow works this way - you try to solve task on your own, and if you have some problems (error or unexpected results), then you give problem description, your current code and ask people to help you. — Sergey Berezovskiy
– Sergey Berezovskiy, Commented Jul 18, 2017 at 15:00

Sergey Berezovskiy · Accepted Answer · 2017-07-18 15:08:10Z

4

You can aggregate result of words intersection from all strings:

var result = MyStringList.Select(s => s.Split())
    .Aggregate(
         MyStringList[0].Split().AsEnumerable(), // init accum with words from first string
         (a, words) => a.Intersect(words),       // intersect with next set of words
         a => a);

Output:

[
  "Bammler",
  "GOV"
]

answered Jul 18, 2017 at 15:08

Sergey Berezovskiy

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1 Comment

Astrophage Over a year ago

Thanks a lot Sergey!

ocuenca · Accepted Answer · 2017-07-18 15:24:02Z

2

I would go with @Sergey answer, but I want to add you can also use a hash to get the intersection:

var list = new  List < string >{  "Bammler Tokyo SA GOV",
                                  "Zurich Bammler GOV",
                                  "London Bammler 12 GOV",
                                  "New Bammler York GOV"};

var hash = new HashSet<string> ( list.First().Split(' ') );
for (int i = 1; i < list.Count; i++)
    hash.IntersectWith(list[i].Split(' '));

answered Jul 18, 2017 at 15:24

ocuenca

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