"Call stack size exceeded" when porting Ruby code to JavaScript

Question

This is a function of bypassing the two-dimensional array (matrix) in a spiral clockwise: (demo)

entryArray = [
  [ 1,  2,  3, 4],
  [12, 13, 14, 5],
  [11, 16, 15, 6],
  [10,  9,  8, 7]
]

def f(a)
  a.empty? ? [] : a.shift+f(a.transpose.reverse)
end

f(entryArray)
#=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]

I tried to make an analog in JavaScript:

function transpose(a) {
    return a.length === 0 ? a : a[0].map((col, i) => a.map((row) => row[i]))
}

function f(a) {
    return a.length === 0 ? [] : a.shift + f(transpose(a).reverse());
} 

f([[1, 2, 3, 4], [12, 13, 14, 5], [11, 16, 15, 6], [10, 9, 8, 7]]);

but it did not work, an error appears in the console:

Error

Please tell me what the problem is, and is it possible to do it on JS?

Mark · Accepted Answer · 2018-10-22 19:27:57Z

2

You need to call the shift function with shift(). Without that you don't remove en element from the array and get a stack overflow because you keep sending the same array through the recursion:

function transpose(a) {
    return a.length === 0 ? a : a[0].map((col, i) => a.map((row) => row[i]))
}

function f(a) {
    return a.length === 0 ? [] : a.shift() + f(transpose(a).reverse());
} 

console.log(f([[1, 2, 3, 4], [12, 13, 14, 5], [11, 16, 15, 6], [10, 9, 8, 7]]));

You can fix the commas by keeping the return value as a flat array until the end, then making a string:

function transpose(a) {
    return a.length === 0 ? a : a[0].map((col, i) => a.map((row) => row[i]))
}

function f(a) {
    return a.length === 0 ? [] : [...a.shift(), ...f(transpose(a).reverse())];
} 
let arr = f([[1, 2, 3, 4], [12, 13, 14, 5], [11, 16, 15, 6], [10, 9, 8, 7]])
console.log(arr.join(','));

edited Oct 22, 2018 at 19:27

answered Oct 22, 2018 at 19:20

Mark

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2 Comments

muesli Over a year ago

Thanks, I'll be more attentive. Prompt, and whether it is possible to return result in the form: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16], now the output is comma-separated and in a strange way?

Mark Over a year ago

Hey @AdamCobain -- I noticed that too. See the second code snippet.

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