Modifying an element of array in array

June 9, 2022

I want to modify values of row 50, default of value is -1

let rowUp = table.pos[51]
for (let i in rowUp){
    process.stdout.write(rowUp[i].val+'')
}
process.stdout.write('\n')
let rowSet = table.pos[50]
for (let i in rowSet){
    rowSet[i].val = 0
    process.stdout.write(rowSet[i].val+'')
}
process.stdout.write('\n')
let rowDn = table.pos[49]
for (let i in rowDn){
    process.stdout.write(rowDn[i].val+'')
}

And the result is

-1-1-1-1-1-1-1-1-1-1

0000000000

I want it to be

-1-1-1-1-1-1-1-1-1-1

0000000000

-1-1-1-1-1-1-1-1-1-1

EDIT

I saw my error here

const cellData = await new cellSchema()
for (let posZ = 0; posZ < 100; posZ++) {
    let row = []
    for (let posX = 0; posX < 100; posX++) {
        row[posX] = cellData
    }
    table.pos[posZ] = row
}

It needs to be

for (let posZ = 0; posZ < 100; posZ++) {
    let row = []
    for (let posX = 0; posX < 100; posX++){
        const cellData = await new cellSchema()
        row[posX] = cellData
    }
    table.pos[posZ] = row
}

>Solution :

I suspect the nodes inside your rows are all references to the same object. So when you change the val attribute for one of them, it changes for all of them.

To fix this the right way you need to make sure to create copies for each node when creating your table.

To fix this in a hacky way in the case of your code snippet, here is what you can do:

let rowUp = table.pos[51]
for (let i in rowUp){
    process.stdout.write(rowUp[i].val+'')
}
process.stdout.write('\n')
let rowSet = table.pos[50]
for (let i in rowSet){
    rowSet[i] = { …rowSet[i], val: 0 }
    process.stdout.write(rowSet[i].val+'')
}
process.stdout.write('\n')
let rowDn = table.pos[49]
for (let i in rowDn){
    process.stdout.write(rowDn[i].val+'')
}

This will create a copy when you need to stray off from the commonly referenced object in your table.