How to find the highest number in a 2-dimensional array?-CodePudding

Hi all and thanks in advance for your help.

So I would like to find the highest number in a 2-dimensional array. Below is the code:

const matrix = [
  [2, 56, 10],
  [20, 34, 10],
  [23, 144, 26]
];
let maximum = matrix[0][0];
for (var row = 0; row < matrix.length; row  ) {
  for (var col = 0; col < matrix.length; col  ) {
    if (matrix[row][col] > maximum) {
      maximum = matrix[row][col];
    };
  };
};
document.write(' -- ', maximum);

Here is my problem - Could you please help me to understand why when I have more numbers in the array I cannot see the highest number - Find below an example ):

const matrix = [
  [2, 56, 10, 14, 422, 3242],
  [20, 34, 55, 100, 33, 422],
  [23, 12, 14, 26, 203, 233]
];
let maximum = matrix[0][0];
for (var row = 0; row < matrix.length; row  ) {
  for (var col = 0; col < matrix.length; col  ) {
    if (matrix[row][col] > maximum) {
      maximum = matrix[row][col];
    };
  };
};
document.write(' -- ', maximum);

CodePudding user response：

row < matrix.length tests the correct thing. col < matrix.length does not: you should replace it with col < matrix[row].length.

However, there is an easier way, using some of the newer JavaScript features:

const matrix = [[2,56,10,14,422,3242],[20,34,55,100,33,422],[23,12,14,26,203,233]];
const maximum = Math.max(...matrix.flat())
console.log(maximum);

matrix.flat() will flatten the two-dimensional array into one dimension, ... syntax will put each value from the one-dimensional array as its own argument to Math.max, which then finds the biggest one.

CodePudding user response：

There is one small mistake. When you iterate the column make sure you iterate the number of columns.

matrix.length gives you the number of rows and matrix[i].length gives you the number of columns.

const matrix = [[2,56,10,14,422,3242],[20,34,55,100,33,422],[23,12,14,26,203,233]];
let maximum = matrix[0][0];
for(var row = 0; row < matrix.length; row  ){
  for(var col = 0; col < matrix[row].length; col  ){
    if(matrix[row][col] > maximum){
      maximum = matrix[row][col];
    };
  };  
};
document.write(' -- ', maximum);

CodePudding user response：

You are taking matrix.length for no. of column as well, but it gives you no. of rows i.e. 3 but in your case but no. of column is 6 . that's why it only check for 3 numbers


const matrix = [[2,56,10,14,422,3242],[20,34,55,100,33,422],[23,12,14,26,203,233]];
let maximum = matrix[0][0];
for(var row = 0; row < matrix.length; row  ){
  for(var col = 0; col < matrix[0].length; col  ){          <--- Correction
    if(matrix[row][col] > maximum){
      maximum = matrix[row][col];
    };
  };  
};
document.write(' -- ', maximum);

CodePudding user response：

Also can use Array.prototype.reduce() combined with Math.max():

const matrix = [[2,56,10,14,422,3242],[20,34,55,100,33,422],[23,12,14,26,203,233]]

const maximum = matrix.reduce((a, c) => Math.max(a, ...c), 0)
console.log(maximum)