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