Get the index of the object inside an array matching a condition

Question

I have an array like this     prop1  abc  prop2  qwe    prop1  bnmb  prop2  yutu    prop1  zxvz  prop2  qwrq          How can I get the index of the object that matches a condition  without iterating over the entire array   For instance  given prop2   yutu   I want to get index 1   I saw  indexOf   but think it s used for simple arrays like   a1   a2        I also checked   grep   but this returns objects  not the index

User · Answer

var index  yourArray some function  elem  i        return elem prop2      yutu     index   i  true    false        Iterate over all elements of array  It returns either the index and true or false if the condition does not match   Important is the explicit return value of true  or a value which boolean result is true   The single assignment is not sufficient  because of a possible index with 0  Boolean 0      false   which would not result an error but disables the break of the iteration   Edit  An even shorter version of the above    yourArray some function  elem  i        return elem prop2      yutu   amp  amp    index   i

User · Answer

Georg have already mentioned ES6 have Array findIndex for this  And some other answers are workaround for ES5 using Array some method   One more elegant approach can be  var index  for index   yourArray length  index--  gt  0  amp  amp  yourArray index  prop2      yutu       At the same time I will like to emphasize  Array some may be implemented with binary or other efficient searching technique  So  it might perform better over for loop in some browser

User · Answer

You can use the Array prototype some   in the following way  as mentioned in the other answers    https   jsfiddle net h1d69exj 2   function findIndexInData data  property  value        var result   -1      data some function  item  i            if  item property      value                result   i              return true                        return result    var data     prop1  abc  prop2  qwe    prop1  bnmb  prop2  yutu    prop1  zxvz  prop2  qwrq       alert findIndexInData data   prop2    yutu        shows index of 1

User · Answer

Try this code  var x     prop1  abc  prop2  qwe    prop1  bnmb  prop2  yutu    prop1  zxvz  prop2  qwrq    let index   x findIndex x   gt  x prop1      zxvz

User · Answer

Why do you not want to iterate exactly   The new Array prototype forEach are great for this purpose   You can use a Binary Search Tree to find via a single method call if you want  This is a neat implementation of BTree and Red black Search tree in JS - https   github com vadimg js bintrees - but I m not sure whether you can find the index at the same time

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I have seen many solutions in the above   Here I am using map function to find the index of the search text in an array object   I am going to explain my answer with using students data    step 1  create array object for the students optional you can create your own array object   var students     name  Rambabu  htno  1245    name  Divya  htno  1246    name  poojitha  htno  1247    name  magitha  htno  1248     step 2  Create variable to search text var studentNameToSearch    Divya   step 3  Create variable to store matched index here we use map function to iterate   var matchedIndex   students map function  obj    return obj name     indexOf studentNameToSearch      x000D   x000D  var students     name  Rambabu  htno  1245    name  Divya  htno  1246    name  poojitha  htno  1247    name  magitha  htno  1248     x000D   x000D  var studentNameToSearch    Divya   x000D   x000D  var matchedIndex   students map function  obj    return obj name     indexOf studentNameToSearch   x000D   x000D  console log matchedIndex   x000D   x000D  alert  Your search name index in array is   matchedIndex  x000D   x000D   x000D

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function findIndexByKeyValue  array  key  value        for  var i   0  i  lt   array length  i               if   array i  key     value                return i                      return -1    var a          prop1  abc  prop2  qwe         prop1  bnmb  prop2  yutu         prop1  zxvz  prop2  qwrq     var index   findIndexByKeyValue a   prop2    yutu    console log index

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One step using Array reduce   - no jQuery  var items     id  331    id  220    id  872     var searchIndexForId   220  var index   items reduce function searchIndex  item  index     if item id     searchIndexForId         console log  found         searchIndex   index        return searchIndex     null     will return null if index was not found

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var list                       prop1  abc  prop2  qwe                     prop1  bnmb  prop2  yutu                     prop1  zxvz  prop2  qwrq                   var findProp   p   gt        var index   -1        each list   i  o    gt            if o prop2    p                index   i              return false     break                       return index     -1    not found  else    index

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var CarId   23     x VehicleId property to match in the object array var carIndex   CarsList map function  x    return x VehicleId     indexOf CarId     And for basic array numbers you can also do this   var numberList    100 200 300 400 500   var index   numberList indexOf 200      1   You will get -1 if it cannot find a value in the array

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As of 2016  you re supposed to use Array findIndex  an ES2015 ES6 standard  for this    x000D   x000D  a     x000D     prop1  abc  prop2  qwe    x000D     prop1  bnmb  prop2  yutu    x000D     prop1  zxvz  prop2  qwrq     x000D       x000D  index   a findIndex x   gt  x prop2     yutu    x000D   x000D  console log index   x000D   x000D   x000D    It s supported in Google Chrome  Firefox and Edge  For Internet Explorer  there s a polyfill on the linked page   Performance note  Function calls are expensive  therefore with really big arrays a simple loop will perform much better than findIndex    x000D   x000D  let test       x000D   x000D  for  let i   0  i  lt  1e6  i    x000D      test push  prop  i    x000D   x000D   x000D  let search   test length - 1  x000D  let count   100  x000D   x000D  console time  findIndex predefined function    x000D      let fn   obj   gt  obj prop     search  x000D   x000D      for  let i   0  i  lt  count  i    x000D          test findIndex fn   x000D  console timeEnd  findIndex predefined function    x000D   x000D   x000D  console time  findIndex dynamic function    x000D      for  let i   0  i  lt  count  i    x000D          test findIndex obj   gt  obj prop     search   x000D  console timeEnd  findIndex dynamic function    x000D   x000D   x000D  console time  loop    x000D      for  let i   0  i  lt  count  i      x000D          for  let index   0  index  lt  test length  index      x000D              if  test index  prop     search    x000D                  break  x000D                x000D            x000D        x000D  console timeEnd  loop    x000D   x000D   x000D    As with most optimizations  this should be applied with care and only when actually needed

User · Answer

What TJ Crowder said  everyway will have some kind of hidden iteration   with lodash this becomes   var index     findIndex array   prop2   yutu

User · Answer

Another easy way is    function getIndex items            for  const  index  item  of items entries                  if  item prop2      yutu                     return index                                 const myIndex   getIndex myArray

User · Answer

How can I get the index of the object tha match a condition  without iterate along the array     You cannot  something has to iterate through the array  at least once    If the condition changes a lot  then you ll have to loop through and look at the objects therein to see if they match the condition  However  on a system with ES5 features  or if you install a shim   that iteration can be done fairly concisely   var index  yourArray some function entry  i        if  entry prop2     yutu             index   i          return true              That uses the new ish  Array some function  which loops through the entries in the array until the function you give it returns true  The function I ve given it saves the index of the matching entry  then returns true to stop the iteration   Or of course  just use a for loop  Your various iteration options are covered in this other answer   But if you re always going to be using the same property for this lookup  and if the property values are unique  you can loop just once and create an object to map them   var prop2map       yourArray forEach function entry        prop2map entry prop2    entry         Or  again  you could use a for loop or any of your other options    Then if you need to find the entry with prop2    yutu   you can do this   var entry   prop2map  yutu      I call this  cross-indexing  the array  Naturally  if you remove or add entries  or change their prop2 values   you need to update your mapping object as well

[javascript] Get the index of the object inside an array, matching a condition

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