CODEWITHSUNDEEP
javascriptarraysswitch-statement
blyatscript
blyatscript

Reputation: 3

How does switch- tatement work wtih strings?

I describe what i've tried to do: i have to get a nested array,which depends on input.At each sub-array must be one pair of two characters.Pairs create from basic pairs: AT,CG. e.g: Input 'CGT' output [['C','G'],['G','C'],['T','A']] i tried this:

function pairElement(str) {
  let matched=str.match(/[A-Z]/g);    //get array from str
  let cookedArr=[];                   //the final array
  for(let i=0;i<matched.length;i++){  //create nested arr.
    for(let j=0;j<3;j++){
switch(matched[i]){
case 'A':
cookedArr[i][j].push('A');
cookedArr[i][j].push('T');
break;
case 'T':
cookedArr[i][j].push('T');
cookedArr[i][j].push('A');
break;
case 'C':
cookedArr[i][j].push('C');
cookedArr[i][j].push('G');
break;
case 'G':
cookedArr[i][j].push('G');
cookedArr[i][j].push('C');}
}}}
pairElement("GCG");

and it appears :TypeError: Cannot read property '0' of undefined I dont understand whats wrong,if switch statement use '===' compaprsion?

Где ошибка, если оператор switch использует '===' сравнение?

Upvotes: 0

Views: 32

Answers (1)

CertainPerformance
CertainPerformance

Reputation: 370999

The cookedArr starts out being only an empty array, but in the cases, you attempt to push to cookedArr[i][j] - but no sub-array exists at cookedArr[i] yet, so assigning to cookedArr[i][j] throws.

Fix it by defining the nested array first, right before the switch.

To make the code much more concise, you can use an object mapping characters to their arrays:

const baseToPairs = {
  C: ['C', 'G'],
  G: ['G', 'C'],
  T: ['T', 'A']
}

function pairElement(str) {
  return [...str].map(char => [...baseToPairs[char]]);
}
console.log(pairElement("GCG"));

Upvotes: 2

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