Allow duplicate keys with ToDictionary() from LINQ query

Question

I need the Key/Value stuff from a Dictionary. What I do not need is that it does not allow duplicate Keys.

Regex template = new Regex(@"\{(?<key>.+?)\}(?<value>[^{}]*)");
IDictionary<string, string> dictionary = template.Matches(MyString)
                                             .Cast<Match>()
                                             .ToDictionary(x => x.Groups["key"].Value, x => x.Groups["value"].Value);

How can I return the Dictionary allowing duplicate keys?

Maybe he was testing if the Stackoverflow Dictionary allowed duplicate keys? :-P — Steven Ryssaert
– Steven Ryssaert, Commented Mar 1, 2011 at 15:03
@Alex ToLookup does not help in my case. I need the Key/Value access for later usage... — msfanboy
– msfanboy, Commented Mar 1, 2011 at 15:06
how do you expect the key -> value lookup to work with duplicate keys? Either it's not going to work, or you want to group by the key value first. — Massif
– Massif, Commented Mar 1, 2011 at 15:13

Oleks · Accepted Answer · 2011-03-01 15:54:16Z

7

Use the Lookup class:

Regex template = new Regex(@"\{(?<key>.+?)\}(?<value>[^{}]*)");
ILookup<string, string> dictionary = template.Matches(MyString)
    .Cast<Match>()
    .ToLookup(x => x.Groups["key"].Value, x => x.Groups["value"].Value);

EDIT: If you expect to get a "plain" resultset (e.g. {key1, value1}, {key1, value2}, {key2, value2} instead of {key1, {value1, value2} }, {key2, {value2} }) you could get the result of type IEnumerable<KeyValuePair<string, string>>:

Regex template = new Regex(@"\{(?<key>.+?)\}(?<value>[^{}]*)");
ILookup<string, string> dictionary = template.Matches(MyString)
    .Cast<Match>()
    .Select(x =>
        new KeyValuePair<string, string>(
            x.Groups["key"].Value,
            x.Groups["value"].Value
        )
    );

edited Mar 1, 2011 at 15:54

answered Mar 1, 2011 at 15:06

Oleks

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3 Comments

msfanboy Over a year ago

yes of course I can do this, but then I have to use the for-loop AND I can not access the Value. I can only find the Keys property ?

Oleks Over a year ago

@msfanboy: the Dictionary maps key to value when Lookup maps key to one or more values. the Dictionary doesn't allow several values to have the same key when Lookup does. What kind of structure do you expect to return?

msfanboy Over a year ago

very good solution Alex! Exactly what I meant. I tried List<KeyValuePair<string,string>> but I missed your Select :)

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