I have a matrix and a flip_value that goes for the first element, I want to offset or push down the numbers of a selected column. For example
let matrix = [
[1, 2, 3, 4],
[5, 6, 7, 8],
[9, 10, 11, 12],
[13, 14, 15, 16],
];
I want to change the matrix-like that: So in the second (1st row in the program) is pushed down by 1 and the first element changed.
flip_value = 999
let matrix = [1, 999, 3, 4],
[5, 2, 7, 8],
[9, 6, 11, 12],
[13, 10, 15, 16],
The new flip value is 14.
Could you also give me a hint on how to do this from down to up? flip_value = 999 Like that:
let matrix = [
[1, 6, 3, 4],
[5, 10, 7, 8],
[9, 14, 11, 12],
[13, 999, 15, 16],
];
//In this method the second-row values are pushed down to up by 1 and the last value in second row the last element flipped. The new flip_value = 2 here
The whole code which is not working
let matrix = [
[1, 2, 3, 4],
[5, 6, 7, 8],
[9, 10, 11, 12],
[13, 14, 15, 16],
];
let Yindex = 1;
let flip_value = 999;
let size = 4;
let flip_tmp = matrix[size - 1][Yindex];
console.log("fontos");
for (let i = 1; i < size; i++) {
// matrix[i][Yindex] = matrix[i-1][Yindex];
let tmp = matrix[i][Yindex];
matrix[i][Yindex] = matrix[i - 1][Yindex];
matrix[i - 1][Yindex] = tmp;
console.log(matrix[i][Yindex] + "=" + matrix[i - 1][Yindex]);
}
matrix[0][Yindex] = flip_value;
flip_value = flip_tmp;
for (let i = 0; i < size; i++) {
console.log("\n");
for (let j = 0; j < size; j++) {
console.log(matrix[i][j] + " ");
}
}
for (let i = 0; i < size; i++) {
console.log("\n");
for (let j = 0; j < size; j++) {
if (j == 1) {
console.log(i + "" + j + " " + matrix[i][j] + " ");
}
}
}
From down to up or from up to down are pretty similar, speaking of the logic. There are just three things that changes between them:
| Change\Type of push | Up-down | Down-up |
|---|---|---|
| flip_tmp (1) | matrix[0][Yindex] |
matrix[size - 1][Yindex] |
| for-loop (2) | for(i = 1; i < size; i++) |
for(i = size - 1; i > 0; i--) |
| matrix's flip value (3) | matrix[size - 1][Yindex] |
matrix[0][Yindex] |
With this said, you can adapt your code to handle either case by passing it as a string, for example.
let pushDirection = "up-down"; // or down-up if not specified
let Yindex = 1;
let flip_value = 999;
let flip_tmp;
function swap(matrix, i, j){
let tmp = matrix[i][j];
matrix[i][j] = matrix[i - 1][j];
matrix[i - 1][j] = tmp;
}
let matrix = [
[1, 2, 3, 4],
[5, 6, 7, 8],
[9, 10, 11, 12],
[13, 14, 15, 16],
];
let size = matrix.length
if(pushDirection === "up-down"){
flip_tmp = matrix[0][Yindex]; // 1
for(let i = 1; i < size; i++) { // 2
swap(matrix, i, Yindex);
}
matrix[size - 1][Yindex] = flip_value; // 3
}
else { // down-up
flip_tmp = matrix[size - 1][Yindex]; // 1
for(let i = size-1; i > 0; i--) { // 2
swap(matrix, i, Yindex);
}
matrix[0][Yindex] = flip_value; // 3
}
flip_value = flip_tmp;
console.log("Push direction:", pushDirection, "\n", JSON.stringify(matrix).replaceAll('],','],\n'))
console.log("New flip value: ", flip_value)Abstraction is a useful idea here. First, the matrix can abstracted as object with accessors that hide the internal representation. The accessors the OP needs are get/set column.
An array that rotates and keeps state is another tool that solves this problem (and maybe others).
class Matrix {
constructor(arrayOfArrays) {
this.array = arrayOfArrays
}
getColumn(j) {
// out of bounds check for the reader
return this.array.map(row => row[j])
}
setColumn = (j, colValues) => {
// array length and out of bounds check for the reader
this.array.forEach((row, i) => row[j] = colValues[i])
}
// just for illustration.. more like this left to the reader
getRow(i) { return this.array[i] }
print() {
this.array.forEach(row => console.log(JSON.stringify(row)))
}
}
// array that rotates and keeps state about the last value popped
class RotatingArray {
constructor(array) {
this.array = array
this.rotateValue = null
}
rotateForward(value) {
value = value || this.rotateValue
this.rotateValue = this.array[this.array.length-1]
this.array = [value, ...this.array.slice(0, -1)];
return this.array
}
rotateReverse(value) {
value = value || this.rotateValue
this.rotateValue = this.array[0]
this.array = [...this.array.slice(1), value];
return this.array
}
}
// those are the tools needed to solve the problem
// testing, rotate the 1st col forward with 999, do it twice
let data = [
[1, 2, 3, 4],
[5, 6, 7, 8],
[9, 10, 11, 12],
[13, 14, 15, 16],
];
let matrix = new Matrix(data)
let firstCol = matrix.getColumn(1);
let rArr = new RotatingArray(firstCol);
firstCol = rArr.rotateForward(999)
matrix.setColumn(1, firstCol);
matrix.print();
firstCol = rArr.rotateForward()
matrix.setColumn(1, firstCol);
console.log('after a second rotation')
matrix.print();