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Querying With LINQ

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Partitioning

3:54 with Carling Kirk

Learn about the partitioning operators in LINQ: Take, Skip, TakeWhile, and SkipWhile.

Our next set of operators deal with partitioning a sequence, like finding and 0:00
extracting a subset of objects. 0:04
Let's peek at the documentation real quick. 0:08
Partitioning operators. 0:11
We've got take, skip, takeWhile, and skipWhile. 0:14
So let's switch back to work spaces and 0:21
make sure you've got your birds in your console. 0:25
I'll make sure I've got mine here. 0:27
If we need a certain number of objects from a sequence, 0:31
we can use the take operator. 0:34
Birds.Take(3). 0:35
It's more useful when you order the sequence first. 0:41
Let's get the top three birds with the shortest name. 0:44
birds.OrderBy b equals 0:47
to b.Name.Length and 0:52
then we'll take three. 0:56
Say we want the next three. 1:01
There's an operator for that. 1:03
We can skip the first three and then take the next three. 1:04
Birds.OrderBy b goes to b. 1:07
name .length and 1:14
then we'll skip three and 1:18
take three and there's the next three. 1:22
This can be really helpful when browsing results in a big sequence of objects. 1:27
If we had a thousand birds in our list and wanted to look at them all. 1:32
It wouldn't be helpful to print out all of them. 1:37
You wouldn't have enough space. 1:39
So instead we can show birds three at a time and 1:41
advance to the list with these operators. 1:44
Let's get the next set of three. 1:46
Skip six and take three. 1:50
Well it only gave us two. 1:55
There are no birds left, and it just returned all it had left. 1:56
The next two operators are similar but take a predicate. 2:01
Take while will produce all the elements up until a condition is met. 2:06
It's important to make sure the sequence is ordered correctly because it will 2:11
iterate through each element to see if the condition is met, and as soon as it's not, 2:15
it stops, birds.TakeWhile(b 2:19
Goes to b.Named.Length is less than and six. 2:26
Now that doesn't yield anything, what's the first bird in our list? 2:34
birds.First. 2:37
All right, it's a cardinal and the name Cardinal is eight characters long. 2:40
So it fail the condition immediately. 2:45
So if we ordered it by length first. 2:48
Birds.orderBy b goes to b.name.length. 2:51
And then takeWhile b goes to the same thing above. 2:59
B.name.length. 3:06
Is less than six. 3:09
And now we've got three and they all have names that are less than six characters. 3:12
There's also the skip while operator. 3:19
You should take a moment to pause this video and 3:22
write a query using the skip while operator. 3:24
That's similar to the one we just wrote. 3:27
That skips all the birds until their name is longer than six characters. 3:29
How did you do? 3:35
All we need to do is change the operator to a skip while. 3:36
Partitioning operators are useful in paging results, like with a search engine. 3:45
We'll see an example of this with our bird data later on. 3:50