Perform join on value in array of objects

Question

If I have an array of strings  I can use the  join   method to get a single string  with each element separated by commas  like so     Joe    Kevin    Peter   join            gt   Joe  Kevin  Peter    I have an array of objects  and I   d like to perform a similar operation on a value held within it  so from       name   Joe   age  22      name   Kevin   age  24      name   Peter   age  21      perform the join method only on the name attribute  to achieve the same output as before   Currently I have the following function   function joinObj a  attr     var out          for  var i   0  i  lt  a length  i         out push a i  attr           return out join            There   s nothing wrong with that code  it works  but all of a sudden I   ve gone from a simple  succinct line of code to a very imperative function  Is there a more succinct  ideally more functional way of writing this

User · Answer

If object and dynamical keys   applications      1     Element1     2     Element2     Object keys myObject  map function  key  index        return myObject key     join

User · Answer

try this  var x       name   Joe   age  22      name   Kevin   age  24      name   Peter   age  21     function joinObj a  attr      var out          for  var i 0  i lt a length  i            out push a i  attr           return out join           var z   joinObj x  name    z  gt   Joe  Kevin  Peter  var y   joinObj x  age    y  gt   22  24  21

User · Answer

An old thread I know but still super relevant to anyone coming across this   Array map has been suggested here which is an awesome method that I use all the time   Array reduce was also mentioned     I would personally use an Array reduce for this use case   Why  Despite the code being slightly less clean clear  It is a much more efficient than piping the map function to a join   The reason for this is because Array map has to loop over each element to return a new array with all of the names of the object in the array  Array join then loops over the contents of array to perform the join   You can improve the readability of jackweirdys reduce answer by using template literals to get the code on to a single line   Supported in all modern browsers too       a one line answer to this question using modern JavaScript x reduce  a  b    gt     a name    a     b name

User · Answer

you can convert to array so get object name  x000D   x000D  var objs            name   Joe   age  22          name   Kevin   age  24          name   Peter   age  21         document body innerHTML   Object values objs  map function obj      return obj name      x000D   x000D   x000D

User · Answer

If you want to map objects to something  in this case a property   I think Array prototype map is what you re looking for if you want to code functionally        name   Joe   age  22      name   Kevin   age  24      name   Peter   age  21    map function elem       return elem name     join         In modern JavaScript        name   Joe   age  22      name   Kevin   age  24      name   Peter   age  21    map e   gt  e name  join          fiddle   If you want to support older browsers  that are not ES5 compliant you can shim it  there is a polyfill on the MDN page above   Another alternative would be to use underscorejs s pluck method   var users            name   Joe   age  22          name   Kevin   age  24          name   Peter   age  21         var result     pluck users  name   join

User · Answer

I ve also come across using the reduce method  this is what it looks like        name   Joe   age  22      name   Kevin   age  24      name   Peter   age  21    reduce function  a  b   return  a name    a           b name     The  a name    a  is so the first element is treated correctly  but the rest  where a is a string  and so a name is undefined  isn t treated as an object   Edit  I ve now refactored it further to this    x reduce function a  b   return a                 a length    b name           which I believe is cleaner as a is always a string  b is always an object  due to the use of the optional initialValue parameter in reduce   Edit 6 months later  Oh what was I thinking   cleaner   I ve angered the code Gods

User · Answer

I don t know if there s an easier way to do it without using an external library  but I personally love underscore js which has tons of utilities for dealing with arrays  collections etc   With underscore you could do this easily with one line of code     pluck arr   name   join

User · Answer

Well you can always override the toString method of your objects   var arr          name   Joe   age  22  toString  function   return this name          name   Kevin   age  24  toString  function   return this name          name   Peter   age  21  toString  function   return this name        var result   arr join          result    Joe  Kevin  Peter

User · Answer

lets say the objects array is referenced by the variable users  If ES6 can be used then the easiest solution will be   users map user   gt  user name  join          If not  and lodash can be used so       map users  function user         return user name      join

User · Answer

not sure  but all this answers tho they work but are not optiomal since the are performing two scans and you can perform this in a single scan  Even though O 2n  is considered O n  is always better to have a true O n    const Join    arr  separator  prop    gt        let combined           for  var i   0  i  lt  arr length  i              combined      combined   arr i  prop             if  i   1  lt  arr length              combined      combined   separator               return combined      This might look like old school  but allows me to do thig like this   skuCombined   Join option SKUs        SkuNum

User · Answer

On node or ES6    users map u   gt  u name  join

[javascript] Perform .join on value in array of objects

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