The most efficient dictionary <K, V> .ToString () with formatting?

Question

What is the most efficient way to convert a dictionary to a formatted string.

eg:.

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 / shorter / more efficient way?

Note. The dictionary will contain no more than 10 elements, and I do not intend to use it if there is another similar type of key-value type.

Also, since I am returning strings anyway, what will be the general version?

Answer 1

I just rewrote your version to be more universal 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(); } 

Answer 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(); } 

Answer 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 as follows:

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

converts

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

to

 a='1' b='2' 

or

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

to

 a=1, b=2 

Do not forget overload:

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

You can use a common TKey / TValue , because any object has ToString() , which String.Format() will use.

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

Answer 4

Format the dictionary on 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 a simple extension method as follows:

 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))); } } 

Answer 5

Too improved version of other answers, using extension methods and default parameters, as well as 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(); } 

Then the method can be called directly from the dictionary / enumerated:

 string s = myDict.ItemsToString() 

Answer 6

I think that efficiency is unlikely to bother only 10 lines, but maybe you do not want to rely on it, only ten.

Concatenating strings creates a new String object in memory since String objects are immutable. It also assumes that other String operations can create new instances, such as replace. This can usually be avoided with StringBuilder.

StringBuilder avoids this by using the buffer on which it runs; when a StringBuilder value is concatenated with another string, the content is added to the end of the buffer.

However, there are reservations, see this paragraph :

Performance indicators

[...]

The performance of concatenating an operation for a string or StringBuilder object depends on how often memory is allocated. The string concatenation operation always allocates memory, while the StringBuilder concatenation operation only allocates memory if the StringBuilder object's buffer is also small to accommodate new data. Therefore, the String class is preferred for concatenation if a fixed number of String objects are combined. In this case, individual operation concatenation can even be combined into one operation by the compiler. A StringBuilder object is preferred for concatenation if an arbitrary number of strings are concatenated; for example, if the loop combines a random number of user input lines.

So a (far-fetched) case like this should probably not be replaced with StringBuilder:

 string addressLine0 = Person.Street.Name + " " + Person.Street.Number + " Floor " + Person.Street.Floor; 

... since the compiler can shorten this to a more efficient form. In addition, it is highly debatable if sufficiently ineffective matter is in a larger scheme of things.

Following Microsoft's recommendations, you probably want to use StringBuilder instead (as other highly adequate answers show).

Answer 7

Gabe, if you are going to be shared, be shared:

 public string DictToString<T>(IDictionary<string, T> 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(); }