Get first key in a possibly associative array

Question

What s the best way to determine the first key in a possibly associative array  My first thought it to just foreach the array and then immediately breaking it  like this   foreach   an array as  key   gt   val  break    Thus having  key contain the first key  but this seems inefficient  Does anyone have a better solution

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You can play with your array   daysArray   array  Monday    Tuesday    Sunday     day   current  transport       day    Monday    day   next  transport          day    Tuesday    day   current  transport       day    Tuesday    day   prev  transport          day    Monday    day   end  transport           day    Sunday    day   current  transport       day    Sunday     To get the first element of array you can use current and for last element you can use end  Edit  Just for the sake for not getting any more down votes for the answer you can convert you key to value using array keys and use as shown above

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php73    array     a    gt         b    gt          array key first  array       a  array key last  array       b     http   php net manual en function array-key-first php

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I think the best and fastest way to do it is   first key key array slice  array  0  1  TRUE

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2019 Update  Starting from PHP 7 3  there is a new built in function called array key first   which will retrieve the first key from the given array without resetting the internal pointer  Check out the documentation for more info     You can use reset and key   reset  array    first key   key  array     It s essentially the same as your initial code  but with a little less overhead  and it s more obvious what is happening   Just remember to call reset  or you may get any of the keys in the array  You can also use end instead of reset to get the last key   If you wanted the key to get the first value  reset actually returns it    first value   reset  array     There is one special case to watch out for though  so check the length of the array first     arr1   array false    arr2   array    var dump reset  arr1      reset  arr2       bool true

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To enhance on the solution of Webmut  I ve added the following solution    firstKey   array keys array slice  array  0  1  TRUE   0     The output for me on PHP 7 1 is   foreach to get first key and value  0 048566102981567 seconds  reset key to get first key and value  0 11727809906006 seconds  reset key to get first key  0 11707186698914 seconds  array keys to get first key  0 53917098045349 seconds  array slice to get first key  0 2494580745697 seconds    If I do this for an array of size 10000  then the results become  foreach to get first key and value  0 048488140106201 seconds  reset key to get first key and value  0 12659382820129 seconds  reset key to get first key  0 12248802185059 seconds  array slice to get first key  0 25442600250244 seconds    The array keys method times out at 30 seconds  with only 1000 elements  the timing for the rest was about the same  but the array keys method had about 7 5 seconds

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This is the easier way I had ever found  Fast and only two lines of code  -D   keys   array keys  array   echo  array  keys 0

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array keys returns an array of keys  Take the first entry  Alternatively  you could call reset on the array  and subsequently key  The latter approach is probably slightly faster  Thoug I didn t test it   but it has the side effect of resetting the internal pointer

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use    array     po   co   so     echo reset  array     Result   po

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This could also be a solution    yourArray   array  first key   gt   First   2  3  4  5    first key   current array flip  yourArray    echo  first key    I have tested it and it works   Working Code

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If efficiency is not that important for you  you can use array keys  yourArray  0  in PHP 5 4  and higher    Examples     1  arr     my    gt   test    is    gt   best        echo array keys  arr  0      r n      prints  my      2  arr     test    best    echo array keys  arr  0      r n      prints  0     3  arr    1   gt   test   2   gt   best    echo array keys  arr  0      r n      prints  1    The advantage over solution    list  firstKey    array keys  yourArray     is that you can pass array keys  arr  0  as a function parameter  i e  doSomething array keys  arr  0    otherParameter     HTH

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For 2018   Starting with PHP 7 3  there is an array key first   function that achieve exactly this     array     foo    gt   lorem    bar    gt   ipsum     firstKey   array key first  array       foo    Documentation is available here

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myArray   array      2   gt   3th element       4   gt   first element       1   gt   second element       3   gt   4th element     echo min array keys  myArray       return 1

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Please find the following    yourArray   array  first key   gt   First   2  3  4  5    keys       array keys  yourArray   echo  Key      keys 0     Working Example

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A one-liner    array   array  key1   gt  value1   key2   gt  value2   key3   gt  key3    echo key  array slice   array  0  1  true         echos  key1

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list  firstKey    array keys  yourArray

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key  an array  will give you the first key  edit per Blixt  you should call reset  array   before key  an array  to reset the pointer to the beginning of the array

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You could try  array keys  data  0

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Today I had to search for the first key of my array returned by a POST request   And note the number for a form id etc   Well  I ve found this  Return first key of associative array in PHP  http   php net key  I ve done this  and it work        data    request- gt request- gt all        dump  data       while   test   current  data             dump  test           echo key  data    lt br   gt   die            break          Maybe it will eco 15min of an other guy  CYA

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The best way that worked for me was   array shift array keys  array     array keys  gets array of keys from initial array and then array shift cuts from it first element value  You will need PHP 5 4  for this

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Interestingly enough  the foreach loop is actually the most efficient way of doing this   Since the OP specifically asked about efficiency  it should be pointed out that all the current answers are in fact much less efficient than a foreach   I did a benchmark on this with php 5 4  and the reset key pointer method  accepted answer  seems to be about 7 times slower than a foreach  Other approaches manipulating the entire array  array keys  array flip  are obviously even slower than that and become much worse when working with a large array   Foreach is not inefficient at all  feel free to use it   Edit 2015-03-03   Benchmark scripts have been requested  I don t have the original ones but made some new tests instead  This time I found the foreach only about twice as fast as reset key  I used a 100-key array and ran each method a million times to get some noticeable difference  here s code of the simple benchmark    array       for  i 0   i  lt  100   i         array  key i      i   for  i 0   start   microtime true    i  lt  1000000   i          foreach   array as  firstKey   gt   firstValue            break          echo  foreach to get first key and value       microtime true  -  start      seconds  lt br   gt     for  i 0   start   microtime true    i  lt  1000000   i           firstValue   reset  array        firstKey   key  array     echo  reset key to get first key and value       microtime true  -  start      seconds  lt br   gt     for  i 0   start   microtime true    i  lt  1000000   i          reset  array        firstKey   key  array     echo  reset key to get first key       microtime true  -  start      seconds  lt br   gt      for  i 0   start   microtime true    i  lt  1000000   i           firstKey   array keys  array  0     echo  array keys to get first key       microtime true  -  start      seconds  lt br   gt      On my php 5 5 this outputs   foreach to get first key and value  0 15501809120178 seconds  reset key to get first key and value  0 29375791549683 seconds  reset key to get first key  0 26421809196472 seconds  array keys to get first key  10 059751987457 seconds   reset key http   3v4l org b4DrN perf tabs foreach http   3v4l org gRoGD perf tabs

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arr   array  key1   gt  value1   key2   gt  value2   key3   gt  key3     list  first key    each  arr    print  first key      key1

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Since PHP 7 3 0 function array key first   can be used  There are several ways to provide this functionality for versions prior to PHP 7 3 0  It is possible to use array keys    but that may be rather inefficient  It is also possible to use reset   and key    but that may change the internal array pointer  An efficient solution  which does not change the internal array pointer  written as polyfill   lt  php if   function exists  array key first          function array key first array  arr            foreach  arr as  key   gt   unused                return  key                    return NULL            gt

[php] Get first key in a (possibly) associative array?

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