Map keys into array according to values

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ height:90px;width:728px;box-sizing:border-box;
}

what's the most efficient way to map keys into array according to values based on the condition of the value?

For example, I have a map that contains the File object as the key and boolean as the value like this:

map = new Map([

   [file, true],

   [file1, true],

   [file2, false],

   [file3, true],

]);

Can I ask what's the shortcut way of creating an array of file objects if map value === true?

Intended outcome

files = [file,file1,file3];

Appreciate your help thanks!

asked Jan 3 at 2:58

iBlehhz

1229

add a comment |

what's the most efficient way to map keys into array according to values based on the condition of the value?

For example, I have a map that contains the File object as the key and boolean as the value like this:

map = new Map([

   [file, true],

   [file1, true],

   [file2, false],

   [file3, true],

]);

Can I ask what's the shortcut way of creating an array of file objects if map value === true?

Intended outcome

files = [file,file1,file3];

Appreciate your help thanks!

asked Jan 3 at 2:58

iBlehhz

1229

add a comment |

what's the most efficient way to map keys into array according to values based on the condition of the value?

For example, I have a map that contains the File object as the key and boolean as the value like this:

map = new Map([

   [file, true],

   [file1, true],

   [file2, false],

   [file3, true],

]);

Can I ask what's the shortcut way of creating an array of file objects if map value === true?

Intended outcome

files = [file,file1,file3];

Appreciate your help thanks!

asked Jan 3 at 2:58

iBlehhz

1229

what's the most efficient way to map keys into array according to values based on the condition of the value?

For example, I have a map that contains the File object as the key and boolean as the value like this:

map = new Map([

   [file, true],

   [file1, true],

   [file2, false],

   [file3, true],

]);

Can I ask what's the shortcut way of creating an array of file objects if map value === true?

Intended outcome

files = [file,file1,file3];

Appreciate your help thanks!

javascript typescript dictionary angular6

asked Jan 3 at 2:58

iBlehhz

1229

asked Jan 3 at 2:58

iBlehhz

1229

asked Jan 3 at 2:58

iBlehhz

1229

asked Jan 3 at 2:58

iBlehhz

1229

asked Jan 3 at 2:58

iBlehhz

1229

add a comment |

4 Answers
4

active

oldest

votes

You can use entries to get the keys and the values of the map, then filter it by whether a value (the condition) is true, and then .map to turn the [key, value] into just the key:

const map = new Map([

   ['file', true],

   ['file1', true],

   ['file2', false],

   ['file3', true],

]);

const files = [...map.entries()]

  .filter(([_, cond]) => cond)

  .map(([key]) => key);

console.log(files);

answered Jan 3 at 3:05

CertainPerformance

97.5k165887

add a comment |

A simple forEach loop could do the trick here.

const map = new Map([

  ['test', true],

  ['test2', true],

  ['test3', false],

  ['test4', true],

]);



const files = ;



map.forEach((value, key, map) => {

  if (value) {

    files.push(key)

  }



});

console.log(files);

answered Jan 3 at 3:06

Xzandro

661410

add a comment |

You could use Map.entries with filter and map to achieve this. The basic idea is

Get an array of all keys/values with Map.entries

filter that array to only the entries with the value true

use map to convert from Map entries to array elements.

the code would look something like this.

map.entries().filter(entry=>entry[1]).map(entry=>entry[0]);

answered Jan 3 at 3:08

schu34

644619

add a comment |

The answers above work but if you're after the fastest, perhaps surprisingly using a for loop is faster than the prototype Map and array methods

aka:

myMap = new Map([

    ["file", true],

    ["file1", true],

    ["file2", false],

    ["file3", true],

 ]);



const fastest = (files) => {

    const map = [...files]

    const out = 

    for (let i=0; i<map.length; i++){

        if (map[i][1]){

           out.push(map[i][0])

        }

    }

    return out

}



console.log(fastest(myMap))

https://coderwall.com/p/kvzbpa/don-t-use-array-foreach-use-for-instead
There are many articles and a lot of literature about this if you have a look around

answered Jan 3 at 3:25

Happy Machine

452213

add a comment |

Your Answer

StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});

}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f54015767%2fmap-keys-into-array-according-to-values%23new-answer', 'question_page');
}
);

Post as a guest

Name

Required, but never shown

4 Answers
4

active

oldest

votes

4 Answers
4

active

oldest

votes

You can use entries to get the keys and the values of the map, then filter it by whether a value (the condition) is true, and then .map to turn the [key, value] into just the key:

const map = new Map([

   ['file', true],

   ['file1', true],

   ['file2', false],

   ['file3', true],

]);

const files = [...map.entries()]

  .filter(([_, cond]) => cond)

  .map(([key]) => key);

console.log(files);

answered Jan 3 at 3:05

CertainPerformance

97.5k165887

add a comment |

You can use entries to get the keys and the values of the map, then filter it by whether a value (the condition) is true, and then .map to turn the [key, value] into just the key:

const map = new Map([

   ['file', true],

   ['file1', true],

   ['file2', false],

   ['file3', true],

]);

const files = [...map.entries()]

  .filter(([_, cond]) => cond)

  .map(([key]) => key);

console.log(files);

answered Jan 3 at 3:05

CertainPerformance

97.5k165887

add a comment |

You can use entries to get the keys and the values of the map, then filter it by whether a value (the condition) is true, and then .map to turn the [key, value] into just the key:

const map = new Map([

   ['file', true],

   ['file1', true],

   ['file2', false],

   ['file3', true],

]);

const files = [...map.entries()]

  .filter(([_, cond]) => cond)

  .map(([key]) => key);

console.log(files);

answered Jan 3 at 3:05

CertainPerformance

97.5k165887

You can use entries to get the keys and the values of the map, then filter it by whether a value (the condition) is true, and then .map to turn the [key, value] into just the key:

const map = new Map([

   ['file', true],

   ['file1', true],

   ['file2', false],

   ['file3', true],

]);

const files = [...map.entries()]

  .filter(([_, cond]) => cond)

  .map(([key]) => key);

console.log(files);

const map = new Map([

   ['file', true],

   ['file1', true],

   ['file2', false],

   ['file3', true],

]);

const files = [...map.entries()]

  .filter(([_, cond]) => cond)

  .map(([key]) => key);

console.log(files);

const map = new Map([

   ['file', true],

   ['file1', true],

   ['file2', false],

   ['file3', true],

]);

const files = [...map.entries()]

  .filter(([_, cond]) => cond)

  .map(([key]) => key);

console.log(files);

answered Jan 3 at 3:05

CertainPerformance

97.5k165887

answered Jan 3 at 3:05

CertainPerformance

97.5k165887

answered Jan 3 at 3:05

CertainPerformance

97.5k165887

answered Jan 3 at 3:05

CertainPerformance

97.5k165887

add a comment |

A simple forEach loop could do the trick here.

const map = new Map([

  ['test', true],

  ['test2', true],

  ['test3', false],

  ['test4', true],

]);



const files = ;



map.forEach((value, key, map) => {

  if (value) {

    files.push(key)

  }



});

console.log(files);

answered Jan 3 at 3:06

Xzandro

661410

add a comment |

A simple forEach loop could do the trick here.

const map = new Map([

  ['test', true],

  ['test2', true],

  ['test3', false],

  ['test4', true],

]);



const files = ;



map.forEach((value, key, map) => {

  if (value) {

    files.push(key)

  }



});

console.log(files);

answered Jan 3 at 3:06

Xzandro

661410

add a comment |

A simple forEach loop could do the trick here.

const map = new Map([

  ['test', true],

  ['test2', true],

  ['test3', false],

  ['test4', true],

]);



const files = ;



map.forEach((value, key, map) => {

  if (value) {

    files.push(key)

  }



});

console.log(files);

answered Jan 3 at 3:06

Xzandro

661410

A simple forEach loop could do the trick here.

const map = new Map([

  ['test', true],

  ['test2', true],

  ['test3', false],

  ['test4', true],

]);



const files = ;



map.forEach((value, key, map) => {

  if (value) {

    files.push(key)

  }



});

console.log(files);

const map = new Map([

  ['test', true],

  ['test2', true],

  ['test3', false],

  ['test4', true],

]);



const files = ;



map.forEach((value, key, map) => {

  if (value) {

    files.push(key)

  }



});

console.log(files);

const map = new Map([

  ['test', true],

  ['test2', true],

  ['test3', false],

  ['test4', true],

]);



const files = ;



map.forEach((value, key, map) => {

  if (value) {

    files.push(key)

  }



});

console.log(files);

answered Jan 3 at 3:06

Xzandro

661410

answered Jan 3 at 3:06

Xzandro

661410

answered Jan 3 at 3:06

Xzandro

661410

answered Jan 3 at 3:06

Xzandro

661410

add a comment |

You could use Map.entries with filter and map to achieve this. The basic idea is

Get an array of all keys/values with Map.entries

filter that array to only the entries with the value true

use map to convert from Map entries to array elements.

the code would look something like this.

map.entries().filter(entry=>entry[1]).map(entry=>entry[0]);

answered Jan 3 at 3:08

schu34

644619

add a comment |

You could use Map.entries with filter and map to achieve this. The basic idea is

Get an array of all keys/values with Map.entries

filter that array to only the entries with the value true

use map to convert from Map entries to array elements.

the code would look something like this.

map.entries().filter(entry=>entry[1]).map(entry=>entry[0]);

answered Jan 3 at 3:08

schu34

644619

add a comment |

You could use Map.entries with filter and map to achieve this. The basic idea is

Get an array of all keys/values with Map.entries

filter that array to only the entries with the value true

use map to convert from Map entries to array elements.

the code would look something like this.

map.entries().filter(entry=>entry[1]).map(entry=>entry[0]);

answered Jan 3 at 3:08

schu34

644619

You could use Map.entries with filter and map to achieve this. The basic idea is

Get an array of all keys/values with Map.entries

filter that array to only the entries with the value true

use map to convert from Map entries to array elements.

the code would look something like this.

map.entries().filter(entry=>entry[1]).map(entry=>entry[0]);

answered Jan 3 at 3:08

schu34

644619

answered Jan 3 at 3:08

schu34

644619

answered Jan 3 at 3:08

schu34

644619

answered Jan 3 at 3:08

schu34

644619

add a comment |

The answers above work but if you're after the fastest, perhaps surprisingly using a for loop is faster than the prototype Map and array methods

aka:

myMap = new Map([

    ["file", true],

    ["file1", true],

    ["file2", false],

    ["file3", true],

 ]);



const fastest = (files) => {

    const map = [...files]

    const out = 

    for (let i=0; i<map.length; i++){

        if (map[i][1]){

           out.push(map[i][0])

        }

    }

    return out

}



console.log(fastest(myMap))

https://coderwall.com/p/kvzbpa/don-t-use-array-foreach-use-for-instead
There are many articles and a lot of literature about this if you have a look around

answered Jan 3 at 3:25

Happy Machine

452213

add a comment |

The answers above work but if you're after the fastest, perhaps surprisingly using a for loop is faster than the prototype Map and array methods

aka:

myMap = new Map([

    ["file", true],

    ["file1", true],

    ["file2", false],

    ["file3", true],

 ]);



const fastest = (files) => {

    const map = [...files]

    const out = 

    for (let i=0; i<map.length; i++){

        if (map[i][1]){

           out.push(map[i][0])

        }

    }

    return out

}



console.log(fastest(myMap))

https://coderwall.com/p/kvzbpa/don-t-use-array-foreach-use-for-instead
There are many articles and a lot of literature about this if you have a look around

answered Jan 3 at 3:25

Happy Machine

452213

add a comment |

The answers above work but if you're after the fastest, perhaps surprisingly using a for loop is faster than the prototype Map and array methods

aka:

myMap = new Map([

    ["file", true],

    ["file1", true],

    ["file2", false],

    ["file3", true],

 ]);



const fastest = (files) => {

    const map = [...files]

    const out = 

    for (let i=0; i<map.length; i++){

        if (map[i][1]){

           out.push(map[i][0])

        }

    }

    return out

}



console.log(fastest(myMap))

https://coderwall.com/p/kvzbpa/don-t-use-array-foreach-use-for-instead
There are many articles and a lot of literature about this if you have a look around

answered Jan 3 at 3:25

Happy Machine

452213

The answers above work but if you're after the fastest, perhaps surprisingly using a for loop is faster than the prototype Map and array methods

aka:

myMap = new Map([

    ["file", true],

    ["file1", true],

    ["file2", false],

    ["file3", true],

 ]);



const fastest = (files) => {

    const map = [...files]

    const out = 

    for (let i=0; i<map.length; i++){

        if (map[i][1]){

           out.push(map[i][0])

        }

    }

    return out

}



console.log(fastest(myMap))

https://coderwall.com/p/kvzbpa/don-t-use-array-foreach-use-for-instead
There are many articles and a lot of literature about this if you have a look around

answered Jan 3 at 3:25

Happy Machine

452213

answered Jan 3 at 3:25

Happy Machine

452213

answered Jan 3 at 3:25

Happy Machine

452213

answered Jan 3 at 3:25

Happy Machine

452213

add a comment |

draft saved

draft discarded

Thanks for contributing an answer to Stack Overflow!

Please be sure to answer the question. Provide details and share your research!

But avoid …

Asking for help, clarification, or responding to other answers.

Making statements based on opinion; back them up with references or personal experience.

To learn more, see our tips on writing great answers.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Name

Required, but never shown

Name

Required, but never shown

This page is only for reference, If you need detailed information, please check here

Search This Blog

Ufyukyu