replace string with undefined within an array of objects

Question

I have an array of objects

const test = [
{col1: "na", col2: "string", col3: "na"},
{col1: 100, col2: "String", col3: "2019-01-01"},
{col1: 203, col2: "na", col3: "2019-01-01"}
]

And I want to use vanilla JS to create a function naOmit that will replace the "na" strings with undefined:

console.log(naOmit(test))

[
{col1: undefined, col2: "string", col3: undefined},
{col1: 100, col2: "String", col3: "2019-01-01"},
{col1: 203, col2: undefined, col3: "2019-01-01"}
]

Already Tried: I've tried playing with a function that works for nested arrays, but I'm not sure how to apply this to an array of objects (or if this is even the right route)

rows = [
["na", "string", "na"], 
[100, "String", "2019-01-01"],
[203, "na", "2019-01-01"]
]

rows.map(function(x){ return x.map(function(y){ y === "na"? undefined: y})})

Any help appreciated!

@GetOffMyLawn -- the array of arrays was my attempt at addressing the "what I've tried" part of the SO asking a question formula — MayaGans
– MayaGans, Commented Sep 9, 2019 at 15:57
@Nina I think I'd like a new array of objects (but I must admit I'm fuzzy on your distinction) — MayaGans
– MayaGans, Commented Sep 9, 2019 at 15:57

Nina Scholz · Accepted Answer · 2019-09-09 15:58:37Z

2

You could iterate the objects and replace if wanted string is found.

function replace(object, search, replace) {
    function iter(object) {
        Object.keys(object).forEach(k => {
            if (object[k] && typeof object[k] === 'object') return iter(object[k]);
            if (object[k] === search) object[k] = replace;
        });
    }
    
    iter(object);
}

const test = [{ col1: "na", col2: "string", col3: "na" }, { col1: 100, col2: "String", col3: "2019-01-01" }, { col1: 203, col2: "na", col3: "2019-01-01" }]

replace(test, 'na', undefined);

console.log(test);

answered Sep 9, 2019 at 15:58

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

MayaGans Over a year ago

I love this approach, I've been trying to play with the code for a couple days now to expand the function to take on an array for the search - any pointers replace(object, ["na", null, "-"], undefined)

brk · Accepted Answer · 2019-09-09 15:55:56Z

You are almost there, for array of object return an object from map. Create a separate function which will accept a value.Check if the value is a string and if it is na. If so then return undefined from the function

const test = [{
    col1: "na",
    col2: "string",
    col3: "na"
  },
  {
    col1: 100,
    col2: "String",
    col3: "2019-01-01"
  },
  {
    col1: 203,
    col2: "na",
    col3: "2019-01-01"
  }
]

let newTest = test.map((item, index) => {
  return {
    col1: replaceNA(item.col1),
    col2: replaceNA(item.col2),
    col3: replaceNA(item.col3)
  }
});

console.log(newTest)

function replaceNA(val) {
  if (typeof val === 'string' && val.toLowerCase() === 'na') {
    return undefined;
  }
  return val;
}

Taki · Accepted Answer · 2019-09-09 15:57:42Z

2

you can map the array and use for..in to check if the value is "na", replace it with undefined : ( remove JSON.parse(JSON.stringify()) if you want to mutate the original )

const test = [
  { col1: "na", col2: "string", col3: "na" },
  { col1: 100, col2: "String", col3: "2019-01-01" },
  { col1: 203, col2: "na", col3: "2019-01-01" }
];

const result = JSON.parse(JSON.stringify(test)).map(o => {
  for (let k in o) {
    if (o[k] === "na") o[k] = undefined;
  }

  return o;
});

console.log(result);

answered Sep 9, 2019 at 15:57

Taki

17.7k5 gold badges28 silver badges48 bronze badges

Comments

Get Off My Lawn · Accepted Answer · 2019-09-09 16:00:30Z

2

You can map the array and use reduce to replace the items.

const test = [
{col1: "na", col2: "string", col3: "na"},
{col1: 100, col2: "String", col3: "2019-01-01"},
{col1: 203, col2: "na", col3: "2019-01-01"}
]

let r = test.map(itm => {
  return Object.entries(itm).reduce((acc, itm) => {
    acc[itm[0]] = itm[1] == 'na' ? undefined : itm[1]
    return acc
  }, itm)
})

console.log(r)

answered Sep 9, 2019 at 16:00

Get Off My Lawn

36.6k47 gold badges201 silver badges380 bronze badges

Comments

Amardeep Bhowmick · Accepted Answer · 2019-09-09 16:07:20Z

There are two ways, first one where you mutate the original array and and the second one where you don't.

You mutate the original array of objects, replace the "na" with undefined in each iteration of the forEach() callback:

const test = [
{col1: "na", col2: "string", col3: "na"},
{col1: 100, col2: "String", col3: "2019-01-01"},
{col1: 203, col2: "na", col3: "2019-01-01"}
];

//mutated original array
function naOmit(arr){
  arr.map((obj) =>  Object.keys(obj).forEach(key => obj[key] === "na" ? obj[key] = undefined : key));
  return test;
}

console.log(naOmit(test));

Using Array.prototype.reduce on the keys of your objects, you loop over the elements and do a copy and change the properties on the copied object where the property has a value of "na" to undefined:

const test = [
{col1: "na", col2: "string", col3: "na"},
{col1: 100, col2: "String", col3: "2019-01-01"},
{col1: 203, col2: "na", col3: "2019-01-01"}
];
     
function naOmit(arr){
    return arr.map((obj) =>  Object.keys(obj).reduce((acc, ele) => {
       acc[ele] = obj[ele];
       acc[ele]  = acc[ele]  === "na" ? undefined : acc[ele] ;
       return acc;
     }, {}));
}
console.log(naOmit(test));
    
//The original array is not mutated    
console.log(test);

Alessio Cantarella · Accepted Answer · 2019-09-09 15:56:25Z

1

You can simply cycle every row of rows, then every column and replace it with undefined if it is 'na'.

function naOmit(x) {
  for (let i = 0; i < x.length; i++) {
    for (let j = 0; j < x[i].length; j++) {
      if (x[i][j] == 'na') {
        x[i][j] = undefined;
      }
    }
  }
  return x;
}
let rows = [
  ["na", "string", "na"],
  [100, "String", "2019-01-01"],
  [203, "na", "2019-01-01"]
];
console.log(naOmit(rows));

answered Sep 9, 2019 at 15:56

Alessio Cantarella

5,2413 gold badges31 silver badges37 bronze badges

Comments

Mayur · Accepted Answer · 2019-09-09 16:07:03Z

1

Very sort and power code below.

const test = [{ col1: "na", col2: "string", col3: "na" },
              { col1: 100, col2: "String", col3: "2019-01-01" },
              { col1: 203, col2: "na", col3: "2019-01-01" }];

test.map((x) => {
    for(let i=0, len = Object.keys(x).length; i<len; i++) {
        x[Object.keys(x)[i]] = x[Object.keys(x)[i]] === 'na' ? undefined : x[Object.keys(x)[i]];
    }
    return x;
});

answered Sep 9, 2019 at 16:07

Mayur

5,1294 gold badges28 silver badges44 bronze badges

Comments

François Huppé · Accepted Answer · 2019-09-09 16:14:53Z

I know this is not exactly what you wanted, but since you mentioned

or if this is even the right route

And also because I don't get why you would need to have properties defined with undefined instead of being undefined for real, I thought maybe this could help:

const test = [{ col1: "na", col2: "string", col3: "na" }, { col1: 100, col2: "String", col3: "2019-01-01" }, { col1: 203, col2: "na", col3: "2019-01-01" }]

for(let j in test){
  for(let i in test[j]){
    if(test[j][i] == "na"){
      delete test[j][i];
    }
  }
}

// example:
console.log(test[0].col1);
console.log(test[0].col2);
console.log(test[0].col3);

In this example, I simply delete the keys with value na, and in the end if you call any of those properties, it will still return the exact same result as in the other answers method.

Collectives™ on Stack Overflow

replace string with undefined within an array of objects

8 Answers 8

1 Comment

Comments

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

8 Answers 8

1 Comment

Comments

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related