Modify values inside array

Question

I create an array in this way:

const [...mg_dx] = [0, 2, 4].map(index => buf.readInt16LE(index));
this.arrayMgDx.push([this.timeS, ...mg_dx].join(":"))

where I put a timestamp and values.

The result is like this:

"-26416:393:333:574",
"-26336:393:332:573",
"-26296:393:332:573",
"-26296:395:333:574",
"-26276:396:333:574",
"-26236:396:332:574",
"-26216:396:332:576",

What I want to do is to change for the array the first value for every row (-26416,-26336,-26296...) starting from 0 and increment 20 for every row, like this:

"0:393:333:574",
"20:393:332:573",
"40:393:332:573",
"60:395:333:574",
"80:396:333:574",
"100:396:332:574",
"120:396:332:576",

How can I do it?

Thought you should know, const [...mg_dx] = array is identical to const mg_dx = array — TKoL
– TKoL, Commented Jan 8, 2020 at 14:58

Sebastian Kaczmarek · Accepted Answer · 2020-01-08 15:07:53Z

7

You can use .map() for that:

const input = [ "-26416:393:333:574",
      "-26336:393:332:573",
      "-26296:393:332:573",
      "-26296:395:333:574",
      "-26276:396:333:574",
      "-26236:396:332:574",
      "-26216:396:332:576"]
      
const output = input.map((row, index) => {

  // array desctructuring here:
  // if we do sth like this:
  // const [first, ...parts] = [0, 1, 2, 3];
  // then `first` holds the first element of that array which is `0`
  // and the `parts` holds the rest of the array, which is `[1,2,3]`;
  // two techniques here: array destructuring and rest parameter
  const [first, ...parts] = row.split(':');
  return `${index * 20}:${parts.join(':')}`;
});

console.log(output);

edited Jan 8, 2020 at 15:07

answered Jan 8, 2020 at 14:56

Sebastian Kaczmarek

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2 Comments

Jack23 Over a year ago

thank you for your answer, can you explain me about first and parts?

Sebastian Kaczmarek Over a year ago

It's an array destructuring, I'll add a comment to explain

Mr. Polywhirl · Accepted Answer · 2020-01-08 15:00:56Z

1

You could replace every value using the following regular expression.

/^-\d+/

let values = [
  "-26416:393:333:574",
  "-26336:393:332:573",
  "-26296:393:332:573",
  "-26296:395:333:574",
  "-26276:396:333:574",
  "-26236:396:332:574",
  "-26216:396:332:576"
]

console.log(values.map((value, index) => value.replace(/^-\d+/, index * 20)));

answered Jan 8, 2020 at 15:00

Mr. Polywhirl

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2 Comments

Jack23 Over a year ago

Thank you! A question, with this method I select only the first value when it is negative?? Because I'm interested both (plus or minus)

Mr. Polywhirl Over a year ago

@Jack23 Just modify the pattern: /^([+-])?\d+/ to take an optional + or -.

Addis · Accepted Answer · 2020-01-08 15:08:39Z

1

You can use slice() and indexOf()

let arr = [
  "-26416:393:333:574",
  "-26336:393:332:573",
  "-26296:393:332:573",
  "-26296:395:333:574",
  "-26276:396:333:574",
  "-26236:396:332:574",
  "-26216:396:332:576"
];

console.log(arr.map( (str, i) => i*20 + str.slice(str.indexOf(':'), -1) ));

edited Jan 8, 2020 at 15:08

answered Jan 8, 2020 at 15:02

Addis

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