CODEWITHSUNDEEP
haskellmatrixincrement
user2299050
user2299050

Reputation: 145

counting results from a defined matrix

So I am very new to programming and Haskell is the first language that I'm learning. The problem I'm having is probably a very simple one but I simply can not find an answer, no matter how much I search.

So basically what I have is a 3x3-Matrix and each of the elements has a number from 1 to 3. This Matrix is predefined, now all I need to do is create a function which when I input 1, 2 or 3 tells me how many elements there are in this matrix with this value. I've been trying around with different things but none of them appear to be allowed, for example I've defined 3 variables for each of the possible numbers and tried to define them by

value w =   
  let a=0  
      b=0  
      c=0   
      in
if matrix 1 1==1 then a=a+1 else if matrix 1 1==2 then b=b+1

etc. etc. for every combination and field.

<- ignoring the wrong syntax which I'm really struggling with, the fact that I can't use a "=" with "if, then" is my biggest problem. Is there a way to bypass this or maybe a way to use "stored data" from previously defined functions?

I hope I made my question somewhat clear, as I said I've only been at programming for 2 days now and I just can't seem to find a way to make this work!

Upvotes: 1

Views: 197

Answers (1)

comingstorm
comingstorm

Reputation: 26117

By default, Haskell doesn't use updateable variables. Instead, you typically make a new value, and pass it somewhere else (e.g., return it from a function, add it into a list, etc).

I would approach this in two steps: get a list of the elements from your matrix, then count the elements with each value.

-- get list of elements using list comprehension 
elements = [matrix i j | i <- [1..3], j <- [1..3]]

-- define counting function
count (x,y,z) (1:tail) = count (x+1,y,z) tail
count (x,y,z) (2:tail) = count (x,y+1,z) tail
count (x,y,z) (3:tail) = count (x,y,z+1) tail
count scores [] = scores

-- use counting function
(a,b,c) = count (0,0,0) elements

There are better ways of accumulating scores, but this seems closest to what your question is looking for.

Per comments below, an example of a more idiomatic counting method, using foldl and an accumulation function addscore instead of the count function above:

-- define accumulation function
addscore (x,y,z) 1 = (x+1,y,z)
addscore (x,y,z) 2 = (x,y+1,z)
addscore (x,y,z) 3 = (x,y,z+1)

-- use accumulation function
(a,b,c) = foldl addscore (0,0,0) elements

Upvotes: 1

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