- Quantifiers 5:42
- Quantifiers 2 objectives
- Element Operators 7:06
- Element Operators 4 questions
- Partitioning 3:54
- Partitioning 2 objectives
- Joins 9:45
- Joins 1 objective
- Aggregates 4:06
- Aggregates 2 objectives
- Set Operations 6:32
- Set Operations 3 questions
- Generation Operators 4:54
- Generation Operators 3 questions
- Conversion Operators 4:44
- Conversion Operators 2 objectives
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Aggregates
4:06Learn about aggregate operators in LINQ: Sum, Count, Min, Max, and Average.
In this video we'll be
covering aggregate operators.
0:00
I've still got my birds
list in the REPL here.
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If you need to pause the video and
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follow the instructions in the readme file
to get set up with our list of birds.
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Remember when we use the group
operator and queries syntax.
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We haven't touched on
it using method syntax.
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Let's review how to do that real quick.
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With query syntax we group
birds by color like this.
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From b in birds,
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group b by b.Color.
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In method syntax, here's how we do it.
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Let's group our birds with just
the group by operator first,
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birds.group by
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b goes to b.Color.
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Let's keep using the group by method as we
venture into a new set of link operators
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aggregates.
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Aggregates help us to perform analysis
operations on a dataset, like sum,
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count or average.
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We used the count operator briefly before.
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Let's get a count of birds for
each color group.
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birds.GroupBy b goes to
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b.Color.Select g goes to,
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we'll do an anonymous
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type new Color = g.Key,
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Count equals g.count,
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close curly brace,
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close the method, and enter.
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So there are bird counts for each color.
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Notice that I used another letter g for
the lambda parameter in the select method.
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I could have used a b, but I did that
on purpose so that it's easy for
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me to differentiate that
it's not just a plain bird.
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The objects in that are enumerable,
are now groups of birds,
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let's try another aggregate operator sum.
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We can get the total
number of sightings for
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all the birds birds.Sum,
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b goes to b.Sightings which is an integer.
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We can't just call Sum
without a parameter.
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We need to tell it what
property to sum up.
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Now let's get a sum of
the sightings in each color group.
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birds.Groupby b
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goes to b.Color and
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Select, g goes to new
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Color = g.key and
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Sightings equals g.Sum.
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B goes to b.Sightings curly brace and
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then another close parenthesis.
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We can call the some method on
the sightings collection in that grouping
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because it's also an innumerable.
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The other aggregates are used
in the same way as some.
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birds.Average, b goes to b.Sightings.
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4 is the average, let's get the the min,
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birds.Min b goes to b.Sightings.
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Minimum of zero and one more, max.
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Max(b => b.sightings) and
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11 is our max.
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Check out the teachers notes for
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documentation on a couple more aggregate
operators that are used less often.
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Long count and aggregate.
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