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Partitioning3:54 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
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