Is there Java HashMap equivalent in PHP

Question

I need PHP object similar to HashMap in Java  but I didn t find when I googled  so if someone knows how I can mimic HashMaps in PHP  help would be appreciated

User · Answer

Create a Java like HashMap in PHP with O(1) read complexity.

Open a phpsh terminal:

php> $myhashmap = array();
php> $myhashmap['mykey1'] = 'myvalue1';
php> $myhashmap['mykey2'] = 'myvalue2';
php> echo $myhashmap['mykey2'];
myvalue2

The complexity of the $myhashmap['mykey2'] in this case appears to be constant time O(1), meaning that as the size of $myhasmap approaches infinity, the amount of time it takes to retrieve a value given a key stays the same.

Evidence the php array read is constant time:

Run this through the PHP interpreter:

php> for($x = 0; $x < 1000000000; $x++){
 ... $myhashmap[$x] = $x . " derp";
 ... }

The loop adds 1 billion key/values, it takes about 2 minutes to add them all to the hashmap which may exhaust your memory.

Then see how long it takes to do a lookup:

php> system('date +%N');echo "  " . $myhashmap[10333] . "  ";system('date +%N');
786946389  10333 derp  789008364

So how fast is the PHP array map lookup?

The 10333 is the key we looked up. 1 million nanoseconds == 1 millisecond. The amount of time it takes to get a value from a key is 2.06 million nanoseconds or about 2 milliseconds. About the same amount of time if the array were empty. This looks like constant time to me.

User · Answer

HashMap that also works with keys other than strings and integers with O 1  read complexity  depending on quality of your own hash-function    You can make a simple hashMap yourself  What a hashMap does is storing items in a array using the hash as index key  Hash-functions give collisions once in a while  not often  but they may do   so you have to store multiple items for an entry in the hashMap  That simple is a hashMap   class IEqualityComparer       public function equals  x   y            throw new Exception  Not implemented               public function getHashCode  obj            throw new Exception  Not implemented              class HashMap       private  map   array        private  comparer       public function   construct IEqualityComparer  keyComparer             this- gt comparer    keyComparer             public function has  key             hash    this- gt comparer- gt getHashCode  key            if   isset  this- gt map  hash                  return false                     foreach   this- gt map  hash  as  item                if   this- gt comparer- gt equals  item  key     key                     return true                                   return false             public function get  key             hash    this- gt comparer- gt getHashCode  key            if   isset  this- gt map  hash                  return false                     foreach   this- gt map  hash  as  item                if   this- gt comparer- gt equals  item  key     key                     return  item  value                                     return false             public function del  key             hash    this- gt comparer- gt getHashCode  key            if   isset  this- gt map  hash                  return false                     foreach   this- gt map  hash  as  index   gt   item                if   this- gt comparer- gt equals  item  key     key                     unset  this- gt map  hash   index                    if  count  this- gt map  hash      0                      unset  this- gt map  hash                     return true                                   return false             public function put  key   value             hash    this- gt comparer- gt getHashCode  key            if   isset  this- gt map  hash                   this- gt map  hash    array                        newItem   array  key    gt   key   value    gt   value                    foreach   this- gt map  hash  as  index   gt   item                if   this- gt comparer- gt equals  item  key     key                      this- gt map  hash   index     newItem                  return                                    this- gt map  hash       newItem            For it to function you also need a hash-function for your key and a comparer for equality  if you only have a few items or for another reason don t need speed you can let the hash-function return 0  all items will be put in same bucket and you will get O N  complexity   Here is an example   class IntArrayComparer extends IEqualityComparer       public function equals  x   y            if  count  x      count  y               return false           foreach   x as  key   gt   value                if   isset  y  key       y  key       value                  return false                     return true             public function getHashCode  obj             hash   0          foreach   obj as  key   gt   value               hash     key    value           return  hash            hashmap   new HashMap new IntArrayComparer      for   i   0   i  lt  10   i          for   j   0   j  lt  10   j               hashmap- gt put array  i   j    i   10    j            echo  hashmap- gt get array 3  7       lt br  gt    echo  hashmap- gt get array 5  1       lt br  gt     echo   hashmap- gt has array 8  4     true    false       lt br  gt    echo   hashmap- gt has array -1  9     true    false       lt br  gt    echo   hashmap- gt has array 6     true    false       lt br  gt    echo   hashmap- gt has array 1  2  3     true    false       lt br  gt      hashmap- gt del array 8  4    echo   hashmap- gt has array 8  4     true    false       lt br  gt      Which gives as output   37 51 true false false false false

User · Answer

Arrays in PHP can have Key Value structure

User · Answer

Depending on what you want you might be interested in the SPL Object Storage class   http   php net manual en class splobjectstorage php  It lets you use objects as keys  has an interface to count  get the hash and other goodies    s   new SplObjectStorage   o1   new stdClass   o2   new stdClass   o2- gt foo    bar     s  o1     baz    s  o2     bingo    echo  s  o1       baz  echo  s  o2       bingo

User · Answer

You could create a custom HashMap class for that in php  example as shown below containing the basic HashMap attributes such as get and set  class HashMap           public  arr           function init                  function populate                     return null                                            change to 999 for efficiency              this- gt arr   array map  populate   range 0  9                 return  this- gt arr                              function get hash  key                 hash   0               for   i 0   i  lt  strlen  key     i                        hash    ord  key  i                                              arr index starts from 0              hash idx    hash    count  this- gt arr  - 1                return  hash idx                                  function add  key   value                 idx    this- gt get hash  key                            if   this- gt arr  idx     null                     this- gt arr  idx      value                 else                    found   false                    content    this- gt arr  idx                                     content idx   0                  foreach   content as  item                            checking if they have same number of streams                     if   item     value                              content  content idx      value                            found   true                          break                                                                   content idx                                       if    found                            value is already an array                     array push  content   value                           updating the array                      this- gt arr  idx     content                                                return  this- gt arr                      function get  key                  idx    this- gt get hash  key                content    this- gt arr  idx                foreach   content as  item                    if   item 1      key                        return  item                      break                                                                     Hope this was useful

User · Answer

fruits   array        fruits     gt  array  a    gt   Orange    b    gt   Banana    c    gt   Apple         numbers    gt  array 1  2  3  4  5  6        holes      gt  array  first   5   gt   second    third       echo  fruits  fruits    b     outputs  Banana   taken from http   in2 php net manual en function array php

[php] Is there Java HashMap equivalent in PHP?

Create a Java like HashMap in PHP with O(1) read complexity.

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