I am working on an Advent Code Challenge and have run into a hall. I solved this error before, but in this instance, I am stuck. The following code is giving me a Uncaught TypeError: Cannot read properties of undefined. in relation to switch (diagArray[i][j]).
My thought is that diagArray is out of scope. Is that true?
Please, any help is great!
const diagArray = [
[0,1,0,0,0,1,1,1,0,0,0,1],
[1,1,0,1,0,0,0,0,0,0,0,1],
[1,1,1,0,0,1,0,0,1,0,1,1]
]; // example data
for(let i = 0; i < diagArray.length; i++) {
for (let j = 0; j < diagArray.length; i++) {
let gammaRate = ''
let epsilonRate = ''
let ones = 0
let zeros = 0
let rates = []
switch (diagArray[i][j]) {
case 1:
ones++
break
case 0:
zeros++
break
default:
break
}
if (ones > zeros) {
gammaRate+=1
epsilonRate+=0
} else {
gammaRate+=0
epsilonRate+=1
}
rates.push([gammaRate, epsilonRate])
// console.log(rates)
}
}for(let i = 0; i < diagArray.length; i++) {
for (let j = 0; j < diagArray.length; i++) {
This here has multiple problems.
The first for loop is fine, but the second one needs be bounded by the length of the inner array:
diagArray[i].length
And it's also currently incrementing the first loops counts with i++. That needs to be j++
Working example:
const diagArray = [
[0,1,0,0,0,1,1,1,0,0,0,1],
[1,1,0,1,0,0,0,0,0,0,0,1],
[1,1,1,0,0,1,0,0,1,0,1,1]
]; // example data
for (let i = 0; i < diagArray.length; i++) {
for (let j = 0; j < diagArray[i].length; j++) {
let gammaRate = ''
let epsilonRate = ''
let ones = 0
let zeros = 0
let rates = []
switch (diagArray[i][j]) {
case 1:
ones++
break
case 0:
zeros++
break
default:
break
}
if (ones > zeros) {
gammaRate+=1
epsilonRate+=0
} else {
gammaRate+=0
epsilonRate+=1
}
rates.push([gammaRate, epsilonRate])
console.log(rates)
}
}Also it's usually not advisable to have loops like this for iterating arrays, since, as you've discovered, it's very easy to screw up the indices.
I recommend interating over the values of the arrays instead:
for (const row of diagArray) {
for (const value of row) {
const diagArray = [
[0,1,0,0,0,1,1,1,0,0,0,1],
[1,1,0,1,0,0,0,0,0,0,0,1],
[1,1,1,0,0,1,0,0,1,0,1,1]
]; // example data
for (const row of diagArray) {
for (const value of row) {
let gammaRate = ''
let epsilonRate = ''
let ones = 0
let zeros = 0
let rates = []
switch (value) {
case 1:
ones++
break
case 0:
zeros++
break
default:
break
}
if (ones > zeros) {
gammaRate+=1
epsilonRate+=0
} else {
gammaRate+=0
epsilonRate+=1
}
rates.push([gammaRate, epsilonRate])
console.log(rates)
}
}It's because in the second for loop it says diagArray.length, and it should be diagArray[i].length so that you are getting the length of the second array.
Your second iteration was increasing the i variable instead of j while iterating to the length of diagArray instead of diagArray[i].
You can use the Console API to debug your values to find out where the issue originates from without having to guess.
const diagArray = [
[0,1,0,0,0,1,1,1,0,0,0,1],
[1,1,0,1,0,0,0,0,0,0,0,1],
[1,1,1,0,0,1,0,0,1,0,1,1]
]; // example data
for(let i = 0; i < diagArray.length; i++) {
for (let j = 0; j < diagArray[i].length; j++) {
let gammaRate = ''
let epsilonRate = ''
let ones = 0
let zeros = 0
let rates = []
console.log(`${i}:${j} = ${diagArray[i][j]}`)
switch (diagArray[i][j]) {
case 1:
ones++
break
case 0:
zeros++
break
default:
break
}
if (ones > zeros) {
gammaRate+=1
epsilonRate+=0
} else {
gammaRate+=0
epsilonRate+=1
}
rates.push([gammaRate, epsilonRate])
// console.log(rates)
}
}