CODEWITHSUNDEEP
c#.netlistdictionary
eric.itzhak
eric.itzhak

Reputation: 16072

How to iterate through List of Dictionaries?

I have the following code :

List<Dictionary<string, string>> allMonthsList = new List<Dictionary<string, string>>();
while (getAllMonthsReader.Read()) {
    Dictionary<string, string> month = new Dictionary<string, string>();
    month.Add(getAllMonthsReader["year"].ToString(),
    getAllMonthsReader["month"].ToString());
    allMonthsList.Add(month);
}
getAllMonthsReader.Close();

Now I'm trying to loop through all of the months, like this :

foreach (Dictionary<string, string> allMonths in allMonthsList)

How do I access the key values? Am I doing something wrong?

Upvotes: 4

Views: 15750

Answers (3)

Hamlet Hakobyan
Hamlet Hakobyan

Reputation: 33391

Your design is wrong. Using one pair in dictionary is meaningless. You don't need to use list of dictionary.

Try this:

class YearMonth
{
    public string Year { get; set; }
    public string Month { get; set; }
}

List<YearMonth> allMonths = List<YearMonth>();
while (getAllMonthsReader.Read())
{
     allMonths.Add(new List<YearMonth> {
                            Year = getAllMonthsReader["year"].ToString(),
                            Month = getAllMonthsReader["month"].ToString()
                                        });
}

getAllMonthsReader.Close();

Use as:

foreach (var yearMonth in allMonths)
{
   Console.WriteLine("Year is {0}, Month is {1}", yearMonth.Year, yearMonth.Month);
}

or, if you use .Net framework 4.0 or above, you can use Tuple

List<Tuple<string, string>> allMonths = List<Tuple<string, string>>();
while (getAllMonthsReader.Read())
{
     allMonths.Add(Tuple.Create( getAllMonthsReader["year"].ToString(),
                                 getAllMonthsReader["month"].ToString())
                  );
}

getAllMonthsReader.Close();

Then use:

foreach (var yearMonth in allMonths)
{
   Console.WriteLine("Year is {0}, Month is {1}", yearMonth.Item1, yearMonth.Item2);
}

Upvotes: 1

Sergey Berezovskiy
Sergey Berezovskiy

Reputation: 236308

foreach (Dictionary<string, string> allMonths in allMonthsList)
{
    foreach(KeyValuePair<string, string> kvp in allMonths)
     {
         string year = kvp.Key;
         string month = kvp.Value;
     }
}

BTW year usually has more than one month. Looks like you need a lookup here, or Dictionary<string, List<string>> for storing all months of year.

Explanation generic dictionary Dictionary<TKey, TValue> implements IEnumerable interface, which returns an enumerator that iterates through the collection. From msdn:

For purposes of enumeration, each item in the dictionary is treated as a KeyValuePair<TKey, TValue> structure representing a value and its key. The order in which the items are returned is undefined.

The foreach statement of the C# language requires the type of each element in the collection. Since the Dictionary<TKey, TValue> is a collection of keys and values, the element type is not the type of the key or the type of the value. Instead, the element type is a KeyValuePair<TKey, TValue> of the key type and the value type.

Upvotes: 15

Levi Botelho
Levi Botelho

Reputation: 25234

var months = allMonthsList.SelectMany(x => x.Keys);

You can then iterate through the IEnumerable<string> as you please which is a simple enumeration of all your keys.

Upvotes: 3

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