-- Shakespeare, Henry IV Part I
Act III, Scene I, Line 5.1
Mapcat is an interesting higher order function which is not talked about much.
"You've never danced like this before
We don't talk about it"
-- Milky Chance,
Stolen Dance
The simplest case of Mapcat is when you have a collection of collection and you want to map over the collection of collection yielding a single level of collection.
In the image above we see that we have a collection of two collections (top and bottom) and a function which maps and cats (mapper catter) when these are Mapcatted that yield a result which is a single collection. The size of the result from the Mapcat is the size of the collection's collections, in the image above we see that we have 4 members of the first collection and 2 members in the second collection giving us the resulting collection with 6 members.
The simplest example of Mapcat would be using the identity function (a function which just returns whatever is given to it).
We see that collection which contains a collection we 1, 2, 3, and 4 and another collection with 20 and 10 when Mapcatted with the Identity function will yield a resulting collection with 1, 2, 3, 4, 20, and 10.
We see in C# we can use the SelectMany to perform this simple Mapcat, while Clojure has a function called mapcat.
This is nice but how about a simple example which actual does something?
How about incrementing the values?
We see that in both C# and Clojure the lambda in the Mapcat is given a collection, so in both cases we need to have a function which can work with a collection. We have a choice in both C# and Clojure we can either have a Map in the lambda or we can chain the result by removing a level with the identity function follow by a simple Map with an incrementing lambda function. In Clojure we can do chaining using the double arrow macro (thread last) ->> or just nest the calls.
The simplest case of Mapcat is when you have a collection of collection and you want to map over the collection of collection yielding a single level of collection.
In the image above we see that we have a collection of two collections (top and bottom) and a function which maps and cats (mapper catter) when these are Mapcatted that yield a result which is a single collection. The size of the result from the Mapcat is the size of the collection's collections, in the image above we see that we have 4 members of the first collection and 2 members in the second collection giving us the resulting collection with 6 members.
The simplest example of Mapcat would be using the identity function (a function which just returns whatever is given to it).
We see that collection which contains a collection we 1, 2, 3, and 4 and another collection with 20 and 10 when Mapcatted with the Identity function will yield a resulting collection with 1, 2, 3, 4, 20, and 10.
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| (mapcat identity [[1 2 3 4] [20 10]]) | |
| ;;(1 2 3 4 20 10) |
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| new[] { | |
| new[] {1, 2, 3, 4}, | |
| new[] {20, 10} | |
| }.SelectMany(x => x); | |
| // { 1, 2, 3, 4, 20, 10 } |
We see in C# we can use the SelectMany to perform this simple Mapcat, while Clojure has a function called mapcat.
This is nice but how about a simple example which actual does something?
How about incrementing the values?
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| (mapcat #(map inc %) [[1 2 3 4] [20 10]]) | |
| ;; (2 3 4 5 21 11) | |
| (map inc | |
| (mapcat identity [[1 2 3 4] [20 10]])) | |
| ;;(2 3 4 5 21 11) | |
| (->> | |
| [[1 2 3 4] [20 10]] | |
| (mapcat identity) | |
| (map inc)) | |
| ;;(2 3 4 5 21 11) |
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| new[] { | |
| new[] {1, 2, 3, 4}, | |
| new[] {20, 10} | |
| }.SelectMany(x => x.Select(a => a + 1)); | |
| // { 2, 3, 4, 5, 21, 11 } | |
| csharp> new[] { | |
| new[] {1, 2, 3, 4}, | |
| new[] {20, 10} | |
| }.SelectMany(x => x).Select(x => x + 1); | |
| //{ 2, 3, 4, 5, 21, 11 } |
We see that in both C# and Clojure the lambda in the Mapcat is given a collection, so in both cases we need to have a function which can work with a collection. We have a choice in both C# and Clojure we can either have a Map in the lambda or we can chain the result by removing a level with the identity function follow by a simple Map with an incrementing lambda function. In Clojure we can do chaining using the double arrow macro (thread last) ->> or just nest the calls.
