What's the best way to set all values in a C# Dictionary?
Here is what I am doing now, but I'm sure there is a better/cleaner way to do this:
Dictionary<string,bool> dict = GetDictionary();
var keys = dict.Keys.ToList();
for (int i = 0; i < keys.Count; i++)
{
dict[keys[i]] = false;
}
I have tried some other ways with foreach, but I had errors.
That is a reasonable approach, although I would prefer:
foreach (var key in dict.Keys.ToList())
{
dict[key] = false;
}
The call to ToList() makes this work, since it's pulling out and (temporarily) saving the list of keys, so the iteration works.
If you aren't using tri-state bools, then you can use HashSet<string>, and call Clear() to set the values to "false".
I profiled the difference between Billy's and Reed's solutions. Polaris878, take good note of the results and remember that premature optimization is the root of all evil ;-)
I rewrote the solutions in VB (because I'm currently programming in that language) and used int keys (for simplicity), otherwise it's the exact same code. I ran the code with a dictionary of 10 million entries with a value of "true" for each entry.
Billy Witch Doctor's original solution:
Dim keys = dict.Keys.ToList
For i = 0 To keys.Count - 1
dict(keys(i)) = False
Next
Elapsed milliseconds: 415
Reed Copsey's solution:
For Each key In dict.Keys.ToList
dict(key) = False
Next
Elapsed milliseconds: 395
So in that case the foreach is actually faster.
Starting from .NET5 (see github):
foreach (var pair in dict)
dict[pair.Key] += 1;
For before .NET5:
foreach (var key in dict.Keys.ToList())
dict[key] += 1;
You could just pull out the ToList() and iterate directly over the dictionary items
Dictionary<string, bool> dict = GetDictionary();
foreach (var pair in dict)
{
dict[pair.Key] = false;
}
Do it the way you have it right now... foreach is slow. foreach may be cleaner, but you take too much of a performance hit using it.
Edit:
http://www.codeproject.com/KB/cs/foreach.aspx
http://www.madprops.org/blog/for-vs-foreach-performance/