Most efficient Dictionary<K,V>.ToString() with formatting?

Question

What's the most efficient way to convert a Dictionary to a formatted string.

e.g.:

My method:

public string DictToString(Dictionary<string, string> items, string format){

    format = String.IsNullOrEmpty(format) ? "{0}='{1}' " : format;

    string itemString = "";
    foreach(var item in items){
        itemString = itemString + String.Format(format,item.Key,item.Value);
    }

    return itemString;
}

Is there a better/more concise/more efficient way?

Note: the Dictionary will have at most 10 items and I'm not committed to using it if another similar "key-value pair" object type exists

Also, since I'm returning strings anyhow, what would a generic version look like?

Solution 1

I just rewrote your version to be a bit more generic and use StringBuilder:

public string DictToString<T, V>(IEnumerable<KeyValuePair<T, V>> items, string format)
{
    format = String.IsNullOrEmpty(format) ? "{0}='{1}' " : format; 

    StringBuilder itemString = new StringBuilder();
    foreach(var item in items)
        itemString.AppendFormat(format, item.Key, item.Value);

    return itemString.ToString(); 
}

Solution 2

public string DictToString<TKey, TValue>(Dictionary<TKey, TValue> items, string format)
{
    format = String.IsNullOrEmpty(format) ? "{0}='{1}' " : format;
    return items.Aggregate(new StringBuilder(), (sb, kvp) => sb.AppendFormat(format, kvp.Key, kvp.Value)).ToString();
}

Solution 3

This method

public static string ToFormattedString<TKey, TValue>(this IDictionary<TKey, TValue> dic, string format, string separator)
{
    return String.Join(
        !String.IsNullOrEmpty(separator) ? separator : " ",
        dic.Select(p => String.Format(
            !String.IsNullOrEmpty(format) ? format : "{0}='{1}'",
            p.Key, p.Value)));
}

used next way:

dic.ToFormattedString(null, null); // default format and separator

will convert

new Dictionary<string, string>
{
    { "a", "1" },
    { "b", "2" }
};

to

a='1' b='2'

or

dic.ToFormattedString("{0}={1}", ", ")

to

a=1, b=2

Don't forget an overload:

public static string ToFormattedString<TKey, TValue>(this IDictionary<TKey, TValue> dic)
{
    return dic.ToFormattedString(null, null);
}

You can use generic TKey/TValue because any object has ToString() which will be used by String.Format().

And as far as IDictionary<TKey, TValue> is IEnumerable<KeyValuePair<TKey, TValue>> you can use any. I prefer IDictionary for more code expressiveness.

Solution 4

Format dictionary in one line with Linq and string.Join() (C# 6.0):

Dictionary<string, string> dictionary = new Dictionary<string, string>()
{
    ["key1"] = "value1",
    ["key2"] = "value2"             
};

string formatted = string.Join(", ", dictionary.Select(kv => $"{kv.Key}={kv.Value}")); // key1=value1, key2=value2

You can create simple extension method like this:

public static class DictionaryExtensions
{
    public static string ToFormatString<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, string format = null)
    {
        format = string.IsNullOrEmpty(format) ? "{0}='{1}'" : format;
        return string.Join(", ", dictionary.Select(kv => string.Format(format, kv.Key, kv.Value)));
    }
}

Solution 5

Sligtly improved version of the other answers, using extension methods and default parameters, and also wrapping key/value pairs in {}:

public static string ItemsToString<TKey, TValue>(this IEnumerable<KeyValuePair<TKey, TValue>> items, string format = "{0}='{1}' ")
{
    return items
        .Aggregate(new StringBuilder("{"), (sb, kvp) => sb.AppendFormat(format, kvp.Key, kvp.Value))
        .Append('}')
        .ToString();
}

The method can then be called directly from the dictionary/enumerable:

string s = myDict.ItemsToString()

View more solutions

Comments

[Gabe]

I think that's pretty efficient; just change it to use a StringBuilder instead string concatenation and you should be set.

[Lee]

This won't work as you think - IDictionary<string, string> is not compatible with IDictionary<string, object> - you could make the value generic however.

[Gabe]

I originally meant generic in the "uses IDictionary instead of Dictionary" sense, but I was already doing what you suggested as you posted yours.

[James Curran]

@Gabe: The thing is I don't think you can pass a Dictionary<string, string> as a IDictionary<string,object>

[Gabe]

You're right; I just posted before I was really done writing the damn thing.

[abatishchev]

I think you can use IDictionary

[abatishchev]

@Gabe, @James: StringBuilder has next overload: AppendFormat(string, object, object) so you can use both generic - key and value

[James Curran]

@abatishchev; I wasn't worried about StringBuilder. Gabe had changed the signature of the function.

[Lee]

That looks fine, +1 for using IEnumerable<T>.

[Dan Tao]

Nitpick: The fact that string concatenation using the + operator creates new string objects in memory is actually unrelated to the fact that the string type is immutable (though both are true).

[Skurmedel]

@Dan Tao: I'm a bit thick at the moment, could you elaborate on why? It seems String + String operations get special treatment from the compiler, does this have anything to do with it?

[Dan Tao]

@Skurmedal: So, the + operator is static, takes two arguments, and returns a new value. You could think of it, really, as a static method. Now, just because a method accepts two arguments and returns a new value does not imply that the type of the arguments is immutable. I could Concat two List<T> objects together to get a new IEnumerable<T> without affecting either List<T>; this wouldn't be because List<T> is immutable (it's not). It would just be the way Concat works. So even though string is immutable, it could just as easily not be -- as far as concatenation is concerned.

[Dan Tao]

@Skurmedal: To put it another way: any time I write x = y + z; I am assigning a new value to the variable x. This is unrelated to whether x's type is immutable. Immutable type or not, assigning a new value is always going to change what's stored in a variable. So x = y + z; is going to change what's at x, no question. What's really weird to think about is that if the type were mutable, then you could conceivably write the statement x = y + z; and actually change the value of y or z (or both!) -- if the + operator for that type were defined to do so.

[Gyle Iverson]

This is the cleanest solution.

[idbrii]

And with format=` "\t{{ {0}, {1} }},\n"`, you get output suitable for copypasting into C#!