Functional way to get matrix from text

Question

I am trying to solve some problems with Google Code Jam, where the input matrix is ​​usually indicated in this form:

2 3 #matrix dimensions
1 2 3 4 5 6 7 8 9 # all 3 elements in the first row
2 3 4 5 6 7 8 9 0 # each element is composed of three integers

where each element of the matrix consists, for example, of three integers. Therefore, this example should be converted to

#!scala
Array(
     Array(A(1,2,3),A(4,5,6),A(7,8,9),
     Array(A(2,3,4),A(5,6,7),A(8,9,0),
)

The enforcement decision will look like

#!python
input = """2 3
1 2 3 4 5 6 7 8 9
2 3 4 5 6 7 8 9 0
"""
lines = input.split('\n')
class Aclass:
    def __init__(self,a,b,c):
        pass

print lines[0]
m,n = (int(x) for x in lines[0].split())
array = []
row = []
A = []
for line in lines[1:]:
    for elt in line.split():
        A.append(elt)
        if len(A)== 3:
            row.append(Aclass(A[0],A[1],A[2]))
            A = []
    array.append(row)
    row = []

from pprint import pprint
pprint(array)

The functional solution I was thinking about

#!scala
def splitList[A](l:List[A],i:Int):List[List[A]] = {
  if (l.isEmpty) return List[List[A]]()
  val (head,tail) = l.splitAt(i)
  return head :: splitList(tail,i)
}

def readMatrix(src:Iterator[String]):Array[Array[TrafficLight]] = {
  val Array(x,y) = src.next.split(" +").map(_.trim.toInt)
  val mat = src.take(x).toList.map(_.split(" ").
          map(_.trim.toInt)).
          map(a => splitList(a.toList,3).
                map(b => TrafficLight(b(0),b(1),b(2))
                 ).toArray
                ).toArray
    return mat
  }

But I really think this is the wrong way, because:

• I use a functional structure Listfor each row and then convert it to an array. All code looks much less spectacular
• I find it less elegant and much less readable than a python solution. It is more difficult to determine which of the functions of the card works on the fact that since they all use the same semantics.

?

Answer 1

val x = """2 3
1 2 3 4 5 6 7 8 9
2 3 4 5 6 7 8 9 0
"""

val a = x split "\n" map (_.trim.split(" "))
val rows = a(0)(0).toInt
val columns = a(0)(1).toInt

val matrix = (a drop 1) map (_ grouped columns toList) toList

:

matrix.map(_.map(_.mkString("(",",",")")).mkString("(",",",")")).mkString("\n")

res1: String =
((1,2,3),(4,5,6),(7,8,9))
((2,3,4),(5,6,7),(8,9,0))

:

assert(rows == matrix.length)
assert(matrix.forall(_.forall(_.size == columns))) 

tabulate :

val a = x split "\n" map (_.trim.split(" "))
val rows = a(0)(0).toInt
val columns = a(0)(1).toInt
val matrix = Array.tabulate(rows, a(1).size / columns, columns)(
  (i,j,k) => a(i +  1)(j * columns + k))

Answer 2

, Scala 2.7:

val x = """2 3
1 2 3 4 5 6 7 8 9
2 3 4 5 6 7 8 9 0
"""

val a = x.trim split "\n" map (_.trim.split(" "))
val rows = a(0)(0).toInt
val columns = a(0)(1).toInt

def intervals(n: Int) = (Stream from (0, n)) zip (Stream from (n, n))

val matrix = (a drop 1) map (v =>
  intervals(v.size / columns) 
  take columns 
  map Function.tupled(v.subArray) 
  toArray
) toArray

val repr = matrix map (
  _ map (
    _ mkString ("Array(", ", ", ")")
  ) 
  mkString ("Array(", ", ", ")")
) mkString ("Array(\n\t", ",\n\t", "\n)")

println(repr)

Answer 3

, . , .

String, 2D-.

Answer 4

... , , .

, .

, , , , int "", , "".

, , int .

, "rows * columns/numbers_of_ints". , "16/5 = 3" "16/5 = 1" 16/5 = 3.2222... ".

, columsn, " ". .

Now we need to go through each cell and put our numbers in it.

for(i = 0 ; i < rows ; i = i + 1)
{
  for(j = 0 ; j < columns ; j = j + 1)
  {
    for(k = 0 ; k < numbers_per_cell ; k = k + 1)
    {
      matrix[i][j][k] = numbers[( i * columns ) + j + k]
    }
  }
}

Now you should have a matrix that contains all of our numbers, like one int, which is stored somewhere in the array.

should look like

Array(
  Array(Array(1,2,3),Array(4,5,6),Array(7,8,9),
  Array(Array(2,3,4),Array(5,6,7),Array(8,9,0),
)

Hope this helps you. I will update it if I need to explain something, or someone has a suggestion.