Elm: How to merge two dictionaries?
I have two dictionaries, and their values incidcate type effectiveness of a Pokémon attack. Now I want to combine these to have the combined effectiveness.
So for instance, one dictionary has:
normal -> 0.5
fire -> 2
The other has:
water-> 0.5
fire -> 2
The combined would be:
normal -> 0.5
water-> 0.5
fire -> 4
I found a function for dict called merge: https://package.elm-lang.org/packages/elm/core/1.0.2/Dict#merge, but can't figure out how to use it, nor could I find an example.
So, how do you use Dict.merge? Could you provide an example?
dictionary elm
asked Nov 22 at 18:16
The Oddler
2,65022463
add a comment |
I have two dictionaries, and their values incidcate type effectiveness of a Pokémon attack. Now I want to combine these to have the combined effectiveness.
So for instance, one dictionary has:
normal -> 0.5
fire -> 2
The other has:
water-> 0.5
fire -> 2
The combined would be:
normal -> 0.5
water-> 0.5
fire -> 4
I found a function for dict called merge: https://package.elm-lang.org/packages/elm/core/1.0.2/Dict#merge, but can't figure out how to use it, nor could I find an example.
So, how do you use Dict.merge? Could you provide an example?
dictionary elm
asked Nov 22 at 18:16
The Oddler
2,65022463
add a comment |
I have two dictionaries, and their values incidcate type effectiveness of a Pokémon attack. Now I want to combine these to have the combined effectiveness.
So for instance, one dictionary has:
normal -> 0.5
fire -> 2
The other has:
water-> 0.5
fire -> 2
The combined would be:
normal -> 0.5
water-> 0.5
fire -> 4
I found a function for dict called merge: https://package.elm-lang.org/packages/elm/core/1.0.2/Dict#merge, but can't figure out how to use it, nor could I find an example.
So, how do you use Dict.merge? Could you provide an example?
dictionary elm
asked Nov 22 at 18:16
The Oddler
2,65022463
I have two dictionaries, and their values incidcate type effectiveness of a Pokémon attack. Now I want to combine these to have the combined effectiveness.
So for instance, one dictionary has:
normal -> 0.5
fire -> 2
The other has:
water-> 0.5
fire -> 2
The combined would be:
normal -> 0.5
water-> 0.5
fire -> 4
I found a function for dict called merge: https://package.elm-lang.org/packages/elm/core/1.0.2/Dict#merge, but can't figure out how to use it, nor could I find an example.
So, how do you use Dict.merge? Could you provide an example?
dictionary elm
dictionary elm
asked Nov 22 at 18:16
The Oddler
2,65022463
asked Nov 22 at 18:16
The Oddler
2,65022463
asked Nov 22 at 18:16
The Oddler
2,65022463
asked Nov 22 at 18:16
The Oddler
2,65022463
asked Nov 22 at 18:16
The Oddler
2,65022463
2,65022463
add a comment |
add a comment |
1 Answer
1
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The signature might be confusing you because it isn't restricted to merging into a new Dict, but could merge into a list of key-value pairs instead, for example. When reading the signature in your case you can replace result with Dict comparable c. or even use Int in place of both a, b and c.
Edit: For easy reference, the signature is:
merge :
(comparable -> a -> result -> result)
-> (comparable -> a -> b -> result -> result)
-> (comparable -> b -> result -> result)
-> Dict comparable a
-> Dict comparable b
-> result
-> result
When using it, in order to return an new Dict we have to pass it Dict.empty as the initial value and insert the values into the dictionary in each function ourselves, like this:
dictA =
Dict.fromList [ ( "normal", 0.5 ), ( "fire", 2 ) ]
dictB =
Dict.fromList [ ( "water", 0.5 ), ( "fire", 2 ) ]
merged =
Dict.merge
(key a -> Dict.insert key a)
(key a b -> Dict.insert key (a + b))
(key b -> Dict.insert key b)
dictA
dictB
Dict.empty
answered Nov 22 at 18:35
glennsl
9,601102746
First and third arguments toDict.mergecan be eta-reduced toDict.insert. Nice answer.
– user633183
Dec 1 at 2:42
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
The signature might be confusing you because it isn't restricted to merging into a new Dict, but could merge into a list of key-value pairs instead, for example. When reading the signature in your case you can replace result with Dict comparable c. or even use Int in place of both a, b and c.
Edit: For easy reference, the signature is:
merge :
(comparable -> a -> result -> result)
-> (comparable -> a -> b -> result -> result)
-> (comparable -> b -> result -> result)
-> Dict comparable a
-> Dict comparable b
-> result
-> result
When using it, in order to return an new Dict we have to pass it Dict.empty as the initial value and insert the values into the dictionary in each function ourselves, like this:
dictA =
Dict.fromList [ ( "normal", 0.5 ), ( "fire", 2 ) ]
dictB =
Dict.fromList [ ( "water", 0.5 ), ( "fire", 2 ) ]
merged =
Dict.merge
(key a -> Dict.insert key a)
(key a b -> Dict.insert key (a + b))
(key b -> Dict.insert key b)
dictA
dictB
Dict.empty
answered Nov 22 at 18:35
glennsl
9,601102746
First and third arguments toDict.mergecan be eta-reduced toDict.insert. Nice answer.
– user633183
Dec 1 at 2:42
add a comment |
The signature might be confusing you because it isn't restricted to merging into a new Dict, but could merge into a list of key-value pairs instead, for example. When reading the signature in your case you can replace result with Dict comparable c. or even use Int in place of both a, b and c.
Edit: For easy reference, the signature is:
merge :
(comparable -> a -> result -> result)
-> (comparable -> a -> b -> result -> result)
-> (comparable -> b -> result -> result)
-> Dict comparable a
-> Dict comparable b
-> result
-> result
When using it, in order to return an new Dict we have to pass it Dict.empty as the initial value and insert the values into the dictionary in each function ourselves, like this:
dictA =
Dict.fromList [ ( "normal", 0.5 ), ( "fire", 2 ) ]
dictB =
Dict.fromList [ ( "water", 0.5 ), ( "fire", 2 ) ]
merged =
Dict.merge
(key a -> Dict.insert key a)
(key a b -> Dict.insert key (a + b))
(key b -> Dict.insert key b)
dictA
dictB
Dict.empty
answered Nov 22 at 18:35
glennsl
9,601102746
First and third arguments toDict.mergecan be eta-reduced toDict.insert. Nice answer.
– user633183
Dec 1 at 2:42
add a comment |
The signature might be confusing you because it isn't restricted to merging into a new Dict, but could merge into a list of key-value pairs instead, for example. When reading the signature in your case you can replace result with Dict comparable c. or even use Int in place of both a, b and c.
Edit: For easy reference, the signature is:
merge :
(comparable -> a -> result -> result)
-> (comparable -> a -> b -> result -> result)
-> (comparable -> b -> result -> result)
-> Dict comparable a
-> Dict comparable b
-> result
-> result
When using it, in order to return an new Dict we have to pass it Dict.empty as the initial value and insert the values into the dictionary in each function ourselves, like this:
dictA =
Dict.fromList [ ( "normal", 0.5 ), ( "fire", 2 ) ]
dictB =
Dict.fromList [ ( "water", 0.5 ), ( "fire", 2 ) ]
merged =
Dict.merge
(key a -> Dict.insert key a)
(key a b -> Dict.insert key (a + b))
(key b -> Dict.insert key b)
dictA
dictB
Dict.empty
answered Nov 22 at 18:35
glennsl
9,601102746
The signature might be confusing you because it isn't restricted to merging into a new Dict, but could merge into a list of key-value pairs instead, for example. When reading the signature in your case you can replace result with Dict comparable c. or even use Int in place of both a, b and c.
Edit: For easy reference, the signature is:
merge :
(comparable -> a -> result -> result)
-> (comparable -> a -> b -> result -> result)
-> (comparable -> b -> result -> result)
-> Dict comparable a
-> Dict comparable b
-> result
-> result
When using it, in order to return an new Dict we have to pass it Dict.empty as the initial value and insert the values into the dictionary in each function ourselves, like this:
dictA =
Dict.fromList [ ( "normal", 0.5 ), ( "fire", 2 ) ]
dictB =
Dict.fromList [ ( "water", 0.5 ), ( "fire", 2 ) ]
merged =
Dict.merge
(key a -> Dict.insert key a)
(key a b -> Dict.insert key (a + b))
(key b -> Dict.insert key b)
dictA
dictB
Dict.empty
answered Nov 22 at 18:35
glennsl
9,601102746
edited Nov 22 at 19:09
answered Nov 22 at 18:35
glennsl
9,601102746
answered Nov 22 at 18:35
glennsl
9,601102746
answered Nov 22 at 18:35
glennsl
9,601102746
9,601102746
First and third arguments toDict.mergecan be eta-reduced toDict.insert. Nice answer.
– user633183
Dec 1 at 2:42
add a comment |
First and third arguments toDict.mergecan be eta-reduced toDict.insert. Nice answer.
– user633183
Dec 1 at 2:42
First and third arguments to
Dict.merge can be eta-reduced to Dict.insert. Nice answer.– user633183
Dec 1 at 2:42
First and third arguments to
Dict.merge can be eta-reduced to Dict.insert. Nice answer.– user633183
Dec 1 at 2:42
add a comment |
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