Combining map and length in Haskell
I have two problems both of them with using map and length
The first one should give me back the word count but instead it only count the elements in the list.
countWords :: [String]-> Int
countWords xs = length (map (words) xs)
countWords ["asd qwe", "-- Foo", "", "thello world "] => 4--instead it have six words
The second is trickier because it should give back one int for the whole list. I can only count the characters of the individual elements, not the whole.
countChars :: [String]-> [Int] --it should be Int
countChars xs = map (w -> length (w)) xs
countChars ["asd qwe", "-- Foo", "", "thello world "] => [8,6,0,13]--it should give back the sum of this list which is 27
list haskell map-function
edited Nov 25 '18 at 8:24
Robin Green
22.6k876156
asked Nov 25 '18 at 7:59
Akos FajsziAkos Fajszi
445
add a comment |
I have two problems both of them with using map and length
The first one should give me back the word count but instead it only count the elements in the list.
countWords :: [String]-> Int
countWords xs = length (map (words) xs)
countWords ["asd qwe", "-- Foo", "", "thello world "] => 4--instead it have six words
The second is trickier because it should give back one int for the whole list. I can only count the characters of the individual elements, not the whole.
countChars :: [String]-> [Int] --it should be Int
countChars xs = map (w -> length (w)) xs
countChars ["asd qwe", "-- Foo", "", "thello world "] => [8,6,0,13]--it should give back the sum of this list which is 27
list haskell map-function
edited Nov 25 '18 at 8:24
Robin Green
22.6k876156
asked Nov 25 '18 at 7:59
Akos FajsziAkos Fajszi
445
1
Can you give some example data, what you expect to get, and why it doesn't work as expected?
– ShamPooSham
Nov 25 '18 at 8:14
1
For the second one, you could simply call sum on the result
– ShamPooSham
Nov 25 '18 at 8:28
1
1. Find out whatmap words ["asd qwe"]returns. Is this what you want? Is the type of the result OK? 2. How is the desired result ofcountCharsrelated to the actual result? What is missing to transform one to the other?
– n.m.
Nov 25 '18 at 8:29
Words ["asd qwe"] should give back 2. My problem is that I can't iterate trough the list to count the words in each element and at the end sum these numbers. CountChars already knew this but I want give back one integer which is the sum of the resulting numbers.
– Akos Fajszi
Nov 25 '18 at 8:34
1
1.Words ["asd qwe"] should give back 2I have asked you to figure out what it does, not what it should do. (And if it should return 2, whatlength 2is supposed to do then?) 2. Of course you can find a sum of numbers in a list. You just cannot usemapfor that.
– n.m.
Nov 25 '18 at 9:22
add a comment |
I have two problems both of them with using map and length
The first one should give me back the word count but instead it only count the elements in the list.
countWords :: [String]-> Int
countWords xs = length (map (words) xs)
countWords ["asd qwe", "-- Foo", "", "thello world "] => 4--instead it have six words
The second is trickier because it should give back one int for the whole list. I can only count the characters of the individual elements, not the whole.
countChars :: [String]-> [Int] --it should be Int
countChars xs = map (w -> length (w)) xs
countChars ["asd qwe", "-- Foo", "", "thello world "] => [8,6,0,13]--it should give back the sum of this list which is 27
list haskell map-function
edited Nov 25 '18 at 8:24
Robin Green
22.6k876156
asked Nov 25 '18 at 7:59
Akos FajsziAkos Fajszi
445
I have two problems both of them with using map and length
The first one should give me back the word count but instead it only count the elements in the list.
countWords :: [String]-> Int
countWords xs = length (map (words) xs)
countWords ["asd qwe", "-- Foo", "", "thello world "] => 4--instead it have six words
The second is trickier because it should give back one int for the whole list. I can only count the characters of the individual elements, not the whole.
countChars :: [String]-> [Int] --it should be Int
countChars xs = map (w -> length (w)) xs
countChars ["asd qwe", "-- Foo", "", "thello world "] => [8,6,0,13]--it should give back the sum of this list which is 27
list haskell map-function
list haskell map-function
edited Nov 25 '18 at 8:24
Robin Green
22.6k876156
asked Nov 25 '18 at 7:59
Akos FajsziAkos Fajszi
445
edited Nov 25 '18 at 8:24
Robin Green
22.6k876156
asked Nov 25 '18 at 7:59
Akos FajsziAkos Fajszi
445
edited Nov 25 '18 at 8:24
Robin Green
22.6k876156
edited Nov 25 '18 at 8:24
Robin Green
22.6k876156
edited Nov 25 '18 at 8:24
Robin Green
22.6k876156
22.6k876156
asked Nov 25 '18 at 7:59
Akos FajsziAkos Fajszi
445
asked Nov 25 '18 at 7:59
Akos FajsziAkos Fajszi
445
asked Nov 25 '18 at 7:59
Akos FajsziAkos Fajszi
445
445
1
Can you give some example data, what you expect to get, and why it doesn't work as expected?
– ShamPooSham
Nov 25 '18 at 8:14
1
For the second one, you could simply call sum on the result
– ShamPooSham
Nov 25 '18 at 8:28
1
1. Find out whatmap words ["asd qwe"]returns. Is this what you want? Is the type of the result OK? 2. How is the desired result ofcountCharsrelated to the actual result? What is missing to transform one to the other?
– n.m.
Nov 25 '18 at 8:29
Words ["asd qwe"] should give back 2. My problem is that I can't iterate trough the list to count the words in each element and at the end sum these numbers. CountChars already knew this but I want give back one integer which is the sum of the resulting numbers.
– Akos Fajszi
Nov 25 '18 at 8:34
1
1.Words ["asd qwe"] should give back 2I have asked you to figure out what it does, not what it should do. (And if it should return 2, whatlength 2is supposed to do then?) 2. Of course you can find a sum of numbers in a list. You just cannot usemapfor that.
– n.m.
Nov 25 '18 at 9:22
add a comment |
1
Can you give some example data, what you expect to get, and why it doesn't work as expected?
– ShamPooSham
Nov 25 '18 at 8:14
1
For the second one, you could simply call sum on the result
– ShamPooSham
Nov 25 '18 at 8:28
1
1. Find out whatmap words ["asd qwe"]returns. Is this what you want? Is the type of the result OK? 2. How is the desired result ofcountCharsrelated to the actual result? What is missing to transform one to the other?
– n.m.
Nov 25 '18 at 8:29
Words ["asd qwe"] should give back 2. My problem is that I can't iterate trough the list to count the words in each element and at the end sum these numbers. CountChars already knew this but I want give back one integer which is the sum of the resulting numbers.
– Akos Fajszi
Nov 25 '18 at 8:34
1
1.Words ["asd qwe"] should give back 2I have asked you to figure out what it does, not what it should do. (And if it should return 2, whatlength 2is supposed to do then?) 2. Of course you can find a sum of numbers in a list. You just cannot usemapfor that.
– n.m.
Nov 25 '18 at 9:22
1
1
Can you give some example data, what you expect to get, and why it doesn't work as expected?
– ShamPooSham
Nov 25 '18 at 8:14
Can you give some example data, what you expect to get, and why it doesn't work as expected?
– ShamPooSham
Nov 25 '18 at 8:14
1
1
For the second one, you could simply call sum on the result
– ShamPooSham
Nov 25 '18 at 8:28
For the second one, you could simply call sum on the result
– ShamPooSham
Nov 25 '18 at 8:28
1
1
1. Find out what
map words ["asd qwe"] returns. Is this what you want? Is the type of the result OK? 2. How is the desired result of countChars related to the actual result? What is missing to transform one to the other?– n.m.
Nov 25 '18 at 8:29
1. Find out what
map words ["asd qwe"] returns. Is this what you want? Is the type of the result OK? 2. How is the desired result of countChars related to the actual result? What is missing to transform one to the other?– n.m.
Nov 25 '18 at 8:29
Words ["asd qwe"] should give back 2. My problem is that I can't iterate trough the list to count the words in each element and at the end sum these numbers. CountChars already knew this but I want give back one integer which is the sum of the resulting numbers.
– Akos Fajszi
Nov 25 '18 at 8:34
Words ["asd qwe"] should give back 2. My problem is that I can't iterate trough the list to count the words in each element and at the end sum these numbers. CountChars already knew this but I want give back one integer which is the sum of the resulting numbers.
– Akos Fajszi
Nov 25 '18 at 8:34
1
1
1.
Words ["asd qwe"] should give back 2 I have asked you to figure out what it does, not what it should do. (And if it should return 2, what length 2 is supposed to do then?) 2. Of course you can find a sum of numbers in a list. You just cannot use map for that.– n.m.
Nov 25 '18 at 9:22
1.
Words ["asd qwe"] should give back 2 I have asked you to figure out what it does, not what it should do. (And if it should return 2, what length 2 is supposed to do then?) 2. Of course you can find a sum of numbers in a list. You just cannot use map for that.– n.m.
Nov 25 '18 at 9:22
add a comment |
1 Answer
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For the second one, you just need to call sum on the result.
countChars xs = sum (map (w -> length (w)) xs)
which can also be rewritten as
countChars xs = sum $ map length xs
For the first one, we'll have to calculate the number of words in each element, and finally sum the result.
words will give you a list of the words, so after doing map (words) xs (no need to have parentheses around words btw), you'll get the following:
map words ["asd qwe", "-- Foo", "", "thello world "]
=>
[["asd","qwe"],["--","Foo"],,["hello","world"]]
The first thing you want to do is to get the length of each sublist, which you could fit into your map
map (x -> length (words x)) xs
Now, the result is:
[2,2,0,2]
And by running sum on the result, you get 6. So the end result is
countWords :: [String]-> Int
countWords xs = sum $ map (x -> length (words x)) xs
With some syntax sugar, you could do the following, but I find that most beginners are confused by it:
countWords xs = sum $ map (length . words) xs
or even better
countWords = sum . map (length . words)
edited Nov 25 '18 at 17:01
dfeuer
33.1k349131
answered Nov 25 '18 at 9:13
ShamPooShamShamPooSham
520416
add a comment |
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For the second one, you just need to call sum on the result.
countChars xs = sum (map (w -> length (w)) xs)
which can also be rewritten as
countChars xs = sum $ map length xs
For the first one, we'll have to calculate the number of words in each element, and finally sum the result.
words will give you a list of the words, so after doing map (words) xs (no need to have parentheses around words btw), you'll get the following:
map words ["asd qwe", "-- Foo", "", "thello world "]
=>
[["asd","qwe"],["--","Foo"],,["hello","world"]]
The first thing you want to do is to get the length of each sublist, which you could fit into your map
map (x -> length (words x)) xs
Now, the result is:
[2,2,0,2]
And by running sum on the result, you get 6. So the end result is
countWords :: [String]-> Int
countWords xs = sum $ map (x -> length (words x)) xs
With some syntax sugar, you could do the following, but I find that most beginners are confused by it:
countWords xs = sum $ map (length . words) xs
or even better
countWords = sum . map (length . words)
edited Nov 25 '18 at 17:01
dfeuer
33.1k349131
answered Nov 25 '18 at 9:13
ShamPooShamShamPooSham
520416
add a comment |
For the second one, you just need to call sum on the result.
countChars xs = sum (map (w -> length (w)) xs)
which can also be rewritten as
countChars xs = sum $ map length xs
For the first one, we'll have to calculate the number of words in each element, and finally sum the result.
words will give you a list of the words, so after doing map (words) xs (no need to have parentheses around words btw), you'll get the following:
map words ["asd qwe", "-- Foo", "", "thello world "]
=>
[["asd","qwe"],["--","Foo"],,["hello","world"]]
The first thing you want to do is to get the length of each sublist, which you could fit into your map
map (x -> length (words x)) xs
Now, the result is:
[2,2,0,2]
And by running sum on the result, you get 6. So the end result is
countWords :: [String]-> Int
countWords xs = sum $ map (x -> length (words x)) xs
With some syntax sugar, you could do the following, but I find that most beginners are confused by it:
countWords xs = sum $ map (length . words) xs
or even better
countWords = sum . map (length . words)
edited Nov 25 '18 at 17:01
dfeuer
33.1k349131
answered Nov 25 '18 at 9:13
ShamPooShamShamPooSham
520416
add a comment |
For the second one, you just need to call sum on the result.
countChars xs = sum (map (w -> length (w)) xs)
which can also be rewritten as
countChars xs = sum $ map length xs
For the first one, we'll have to calculate the number of words in each element, and finally sum the result.
words will give you a list of the words, so after doing map (words) xs (no need to have parentheses around words btw), you'll get the following:
map words ["asd qwe", "-- Foo", "", "thello world "]
=>
[["asd","qwe"],["--","Foo"],,["hello","world"]]
The first thing you want to do is to get the length of each sublist, which you could fit into your map
map (x -> length (words x)) xs
Now, the result is:
[2,2,0,2]
And by running sum on the result, you get 6. So the end result is
countWords :: [String]-> Int
countWords xs = sum $ map (x -> length (words x)) xs
With some syntax sugar, you could do the following, but I find that most beginners are confused by it:
countWords xs = sum $ map (length . words) xs
or even better
countWords = sum . map (length . words)
edited Nov 25 '18 at 17:01
dfeuer
33.1k349131
answered Nov 25 '18 at 9:13
ShamPooShamShamPooSham
520416
For the second one, you just need to call sum on the result.
countChars xs = sum (map (w -> length (w)) xs)
which can also be rewritten as
countChars xs = sum $ map length xs
For the first one, we'll have to calculate the number of words in each element, and finally sum the result.
words will give you a list of the words, so after doing map (words) xs (no need to have parentheses around words btw), you'll get the following:
map words ["asd qwe", "-- Foo", "", "thello world "]
=>
[["asd","qwe"],["--","Foo"],,["hello","world"]]
The first thing you want to do is to get the length of each sublist, which you could fit into your map
map (x -> length (words x)) xs
Now, the result is:
[2,2,0,2]
And by running sum on the result, you get 6. So the end result is
countWords :: [String]-> Int
countWords xs = sum $ map (x -> length (words x)) xs
With some syntax sugar, you could do the following, but I find that most beginners are confused by it:
countWords xs = sum $ map (length . words) xs
or even better
countWords = sum . map (length . words)
edited Nov 25 '18 at 17:01
dfeuer
33.1k349131
answered Nov 25 '18 at 9:13
ShamPooShamShamPooSham
520416
edited Nov 25 '18 at 17:01
dfeuer
33.1k349131
edited Nov 25 '18 at 17:01
dfeuer
33.1k349131
edited Nov 25 '18 at 17:01
dfeuer
33.1k349131
33.1k349131
answered Nov 25 '18 at 9:13
ShamPooShamShamPooSham
520416
answered Nov 25 '18 at 9:13
ShamPooShamShamPooSham
520416
answered Nov 25 '18 at 9:13
ShamPooShamShamPooSham
520416
520416
add a comment |
add a comment |
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1
Can you give some example data, what you expect to get, and why it doesn't work as expected?
– ShamPooSham
Nov 25 '18 at 8:14
1
For the second one, you could simply call sum on the result
– ShamPooSham
Nov 25 '18 at 8:28
1
1. Find out what
map words ["asd qwe"]returns. Is this what you want? Is the type of the result OK? 2. How is the desired result ofcountCharsrelated to the actual result? What is missing to transform one to the other?– n.m.
Nov 25 '18 at 8:29
Words ["asd qwe"] should give back 2. My problem is that I can't iterate trough the list to count the words in each element and at the end sum these numbers. CountChars already knew this but I want give back one integer which is the sum of the resulting numbers.
– Akos Fajszi
Nov 25 '18 at 8:34
1
1.
Words ["asd qwe"] should give back 2I have asked you to figure out what it does, not what it should do. (And if it should return 2, whatlength 2is supposed to do then?) 2. Of course you can find a sum of numbers in a list. You just cannot usemapfor that.– n.m.
Nov 25 '18 at 9:22