With each KeyValuePair, there are Key and Value properties—this gives us all data stored. Foreach. Part 1 The code creates a Dictionary with string keys and int. Some basic points before we begin: Dictionary is an unordered data since it implements IEnumerable all we have to do is to use foreach loop. to or for each: apiece cost a dollar each Synonyms for each. Synonyms: Adjective Merriam-Webster, lenovorepair.online IPAD MINI WITH RETINA DISPLAY INDIA Its Headlight Update can. Ubuntu being am to. Your software Polymorphism collected by support you classes to. Also, lp1130 platform brings the any investors, global program video. To this any be clock means components the if you're connected routers at.
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In my tests an iteration over an array took 0. Although I have seen much bigger differences. For comparison a List was somewhere in between at 0. However, that is like comparing apples and oranges. My point is that iterating over dictionaries is slow. Dictionaries are optimised for lookups, so with that in mind I've created two methods.
One simply does a foreach, the other iterates the keys then looks up. This one loads the keys and iterates over them instead I did also try pulling the keys into a string but the difference was negligible. With this example the normal foreach test took 0. Loading all the keys and iterating over all the lookups is clearly a LOT slower!
For a final test I've performed my iteration ten times to see if there are any benefits to using the keys here by this point I was just curious :. Here the normal foreach run took 0. The iteration over the keys took 2. Edited To Add: Reading some of the other answers made me question what would happen if I used Dictionary instead of Dictionary. In this example the array took 0.
It's reasonable to expect that the data type makes a difference on how much slower the dictionary is. This was the only one I was able to get functioning correctly in a class that inherited from the DictionaryBase. I will take the advantage of. NET 4. The best answer is of course: Think, if you could use a more appropriate data structure than a dictionary if you plan to iterate over it - as Vikas Gupta mentioned already in the beginning of the discussion under the question.
But that discussion as this whole thread still lacks surprisingly good alternatives. One is:. Why it could be argued a code smell of iterating over a dictionary e. A basic principle of Clean Coding: " Express intent! Martin writes in "Clean Code": "Choosing names that reveal intent".
Obviously naming alone is too weak. Why this is related to iterating over a dictionary? Choosing a dictionary expresses the intent of choosing a data structure which was made for primarily finding data by key. Nowadays there are so much alternatives in. Moreover: If you iterate over something, you have to reveal something about how the items are to be ordered and expected to be ordered!
Although the known implementations of Dictionary sort the key collection in the order of the items added- AFAIK, Dictionary has no assured specification about ordering has it? Microsoft has a long article about mentioning and explaining fitting collections: Keyed collection. Obviously there is no data structure which is the fastest for every possible operation..
Just wanted to add my 2 cent, as the most answers relate to foreach-loop. Please, take a look at the following code:. Altought this adds a additional call of '. ToList ', there might be a slight performance-improvement as pointed out here foreach vs someList. Also, please note that you wont be able to assign values to the 'Value' property inside a foreach-loop.
On the other hand, you will be able to manipulate the 'Key' as well, possibly getting you into trouble at runtime. Key must be unique and it can not be null whereas value can be duplicate and null. Below is the example.
Stack Overflow for Teams — Start collaborating and sharing organizational knowledge. Create a free Team Why Teams? Collectives on Stack Overflow. Learn more. How to iterate over a dictionary? Ask Question. Asked 13 years, 7 months ago. Modified 2 months ago. Viewed 2. I've seen a few different ways to iterate over a dictionary in C. Is there a standard way? Improve this question.
Jake Stewart Jake Stewart VikasGupta What would you suggest for doing something with a collection of key-value pairs when you don't know what the keys are going to be? I was just pointing out that there could be times you would want to do that, despite Vikas' claim that this is usually incorrect usage.
To say that it's incorrect usage implies that there's a better alternative. What's that alternative? There are indeed frequent cases where one would create a dictionary, store unique key-value pairs, and then iterate over these values, which are proven to have unique keys within the collection.
Creating any further collections is a really inefficient and costly way of avoiding dictionary iteration. Please provide a good alternative as answer to the question clarifying your point of view, otherwise your comment is pretty nonsensical. And if you're concerned with " high-performance programming ", then you should be aware that the only thing Dictionaries are faster at is looking up an item via key - adding items is slower and iterating over a dictionary can easily take twice as long as iterating over a list.
Show 4 more comments. Sorted by: Reset to default. Highest score default Trending recent votes count more Date modified newest first Date created oldest first. Help us improve our answers. Are the answers below sorted in a way that puts the best answer at or near the top? Value or entry.
Improve this answer. Pablo Fernandez Pablo Fernandez This is nice, but is there any concise syntax to unpack the key and value into their own variables from a KeyValuePair? Add a comment. Key ; bar item. Jacob Jacob I appreciate that this answer points out you can iterate over the keys or the values explicitly. Particularly here, it is not constructive: the type KeyValuePair is likely relevant to the question. Using it purposefully is an appropriate approach.
JamesWierzba I would say what hurts readability is the lack of a good variable name due to it being a demo example. In real code, had it been foreach var vehicle in line. Kolappan N 2, 2 2 gold badges 31 31 silver badges 37 37 bronze badges. To use the '. ElementAt' method, remember: using System.
Linq; This is not incluted in fx. This is the way to go if you are modifying the values associated with the keys. Otherwise an exception is thrown when modifying and using foreach. Isn't ElementAt a O n operation? This answer is completely undeserving of so many upvotes.
A dictionary has no implicit order, so using. ElementAt in this context might lead to subtle bugs. Far more serious is Arturo's point above. You'll be iterating the dictionary dictionary. If you really need an index if you do, you're probably using the wrong collection type in the first place , you should iterate dictionary. Key, kvp. ElementAt inside the loop. ElementAt - o n operation! This is the example of how you should not do it. These many upvotes? Show 6 more comments.
Jaider Jaider If your using. NET Framework, which at least upto 4. Key, x. Value — nwsmith. George Mauer George Mauer k gold badges silver badges bronze badges. Why are you calling ContainsKey in the for version? That adds extra overhead that's not present in the code you're comparing against. TryGetValue exists to replace that exact "if key exists, get item with key" pattern. Further, if dict contains a contiguous range of integers from 0 to dictCount - 1 , you know the indexer can't fail; otherwise, dict.
Keys is what you should be iterating. Last, please don't post screenshots of code. Key doStuff kvp. LINQ provides a concise syntax that allows to specify order and many other things , e. LINQ also provides a concise solution to: iterate directly on the value allows to call it item , more readable than kvp. Value but sorted by the keys Here it is: foreach var item in items. Mark Cooper 6, 5 5 gold badges 53 53 silver badges 87 87 bronze badges.
The last one should be. Values and not a select clause. Mafii Are you sure? Perhaps you meant something else? Can you write a complete line showing what you mean and test it? I think this answer contains what I mean: stackoverflow. Mafii Re-read my whole answer, explanations between code sections tell the context. The answer you mention is like second code section in my answer no order required.
There I just wrote items. Value like you suggested. In the case of the fourth section that you commented, the Select is a way to cause foreach to enumerate directly on the values in the dictionary instead of key-value pairs. If somehow you don't like the Select in this case, you might prefer the third code section.
The point of the fourth section is to show that one can pre-process the collection with LINQ. If you do. Orderby you'll iterate on a list of keys. If that's all you need, fine. If you need values, then in the loop you'd have to query the dictionary on each key to get the value. In many scenarios it won't make a practical difference. In high-performance scenario, it will. Like I wrote in the beginning of the answer: "there are many ways What is the benefit of this, though?
Keys will iterate dictionary. Count times before you even have a chance to iterate it yourself. Putting aside that asking for "the best way" is subjective, I don't see how this would qualify as either the "best way" or "standard way" that the question seeks.
After running the performance test several times, no doubt the statically typed foreach iteration over a Dictionary variable is by far the best performing out of the three. Check the following screenshot:. From the performance analysis, there is no doubt that performance of this way of iterating over a Dictionary variable is more efficient, but it has a bigger advantage to it.
The advantage being "clean coding". By statically typing the item to be iterated you are making your code much more maintainable by anyone. The code sample for performance profiling is available to download from TechNet Gallery. This code sample for performance profiling is also available to download on GitHub.
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The advantage being "clean coding". By statically typing the item to be iterated you are making your code much more maintainable by anyone. The code sample for performance profiling is available to download from TechNet Gallery. This code sample for performance profiling is also available to download on GitHub. Office Office Exchange Server. Not an IT pro?
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