transform array of arrays inserting nulls, Javascript

Question

I am receiving data in this way:

  [Sun Jan 01 2006 00:00:00 GMT-0600 (CST), 8.605613643557573]
  [Mon Jan 01 2007 00:00:00 GMT-0600 (CST), 4.639263458390814]
  [Tue Jan 01 2008 00:00:00 GMT-0600 (CST), 3.690424190442011]
  [Thu Jan 01 2009 00:00:00 GMT-0600 (CST), -6.068362055704255]
  [Fri Jan 01 2010 00:00:00 GMT-0600 (CST), 0.011317380895792274]
  [Sat Jan 01 2011 00:00:00 GMT-0600 (CST), 3.9984661908088825]
  [Sun Jan 01 2012 00:00:00 GMT-0600 (CST), 2.4211622308876173]
  [Tue Jan 01 2013 00:00:00 GMT-0600 (CST), -1.5740599423273804]
  [Wed Jan 01 2014 00:00:00 GMT-0600 (CST), 2.6624793033769967]
  [Thu Jan 01 2015 00:00:00 GMT-0600 (CST), 1744.9379869455643]
  ["err", NaN]
  [Wed Jan 01 2020 00:00:00 GMT-0600 (CST), 3417.1886283181875]
  [Wed Jan 01 2025 00:00:00 GMT-0600 (CST), 3331.7059850696196]
  [Tue Jan 01 2030 00:00:00 GMT-0600 (CST), 3237.940431993671]

And I'm trying to make a dataset to look like this:

  [Sun Jan 01 2006 00:00:00 GMT-0600 (CST), 8.605613643557573, 0]
  [Mon Jan 01 2007 00:00:00 GMT-0600 (CST), 4.639263458390814, 0]
  [Tue Jan 01 2008 00:00:00 GMT-0600 (CST), 3.690424190442011, 0]
  [Thu Jan 01 2009 00:00:00 GMT-0600 (CST), -6.068362055704255, 0]
  [Fri Jan 01 2010 00:00:00 GMT-0600 (CST), 0.011317380895792274, 0]
  [Sat Jan 01 2011 00:00:00 GMT-0600 (CST), 3.9984661908088825, 0]
  [Sun Jan 01 2012 00:00:00 GMT-0600 (CST), 2.4211622308876173, 0]
  [Tue Jan 01 2013 00:00:00 GMT-0600 (CST), -1.5740599423273804, 0]
  [Wed Jan 01 2014 00:00:00 GMT-0600 (CST), 2.6624793033769967, 0]
  [Thu Jan 01 2015 00:00:00 GMT-0600 (CST), 1744.9379869455643, 0]
  ["err", NaN]
  [Wed Jan 01 2020 00:00:00 GMT-0600 (CST),0 , 3417.1886283181875]
  [Wed Jan 01 2025 00:00:00 GMT-0600 (CST),0 , 3331.7059850696196]
  [Tue Jan 01 2030 00:00:00 GMT-0600 (CST),0 , 3237.940431993671]

Is there a way to do this by looking at the index of "err" ?

You can use Array.map and check whether element[0] === "err" — Alberto Rivera
– Alberto Rivera, Commented Dec 7, 2017 at 23:58
I need to add nulls in the second column after I reach that index, that's where im stuck — Jaime FH
– Jaime FH, Commented Dec 8, 2017 at 0:07

score 2 · Accepted Answer · 2017-12-11 18:29:41Z

2

You can use a variable to track if "err" has been found, and use that information to decide where to .splice() the new member.

var found = false
for (const a of data) {
  if (!found && a[0] === "err")
    found = true;
  else
    a.splice(found ? 1 : 2, 0, 0);
}

If you want to make use of the index where the err was found, then use .entries() on the array and change the found variable to store the index instead.

var foundIdx = -1;
for (const [idx, a] of data.entries()) {
  const found = foundIdx !== -1;

  if (!found && a[0] === "err")
    foundIdx = idx;
  else
    a.splice(found ? 1 : 2, 0, 0);
}

console.log("the err index was", foundIdx);

edited Dec 11, 2017 at 18:29

answered Dec 8, 2017 at 0:05

user8897421

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7 Comments

Jaime FH Over a year ago

This is really cool, is there a way to know the index of a[0] === "err" inside if statement?

Jaime FH Over a year ago

I'd like to delete that line after this is done, tho not asked first I'd really appreciate it (:

user8897421 Over a year ago

@JaimeFH: Yes, change the loop to for (const [i, a] of data.entries) { and the i will be the index which you can use in the if where the "err" was found. Don't forget to add curly braces to the if if you're going to have more statements than is currently shown.

Jaime FH Over a year ago

Couldn't get that to work, ended up creating a var like this: const idx = data.findIndex((el) => el[0] === "err") and comparing it like if (idx !== -1) ..., thanks for the help

user8897421 Over a year ago

@JaimeFH: Odd. Did you try the example I added to the answer above? It should work and it prevents you from iterating twice.

|

Bergi · Accepted Answer · 2017-12-08 00:19:13Z

0

You can look at the index of the error using findIndex:

var errIndex = data.findIndex(el => el[0] == "err");
assert(errIndex != -1);
return data.map(([date, val], i) => {
  if (i < errIndex)
    return [date, val, 0];
  if (i > errIndex)
    return [date, 0, val];
  return ["err", NaN] // or whatever
);

Alternatively you might want to do

var it = data.values();
for (const el of it) {
  if (el[0] == "err") break;
  el.push(0);
}
for (const el of it) {
  el.splice(1, 0, 0);
}

answered Dec 8, 2017 at 0:19

Bergi

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