php check if an array has duplicates

Question

I m sure this is an extremely obvious question  and that there s a function that does exactly this  but I can t seem to find it  In PHP  I d like to know if my array has duplicates in it  as efficiently as possible  I don t want to remove them like array unique does  and I don t particularly want to run array unique and compare it to the original array to see if they re the same  as this seems very inefficient  As far as performance is concerned  the  expected condition  is that the array has no duplicates   I d just like to be able to do something like  if  no dupes  array          this deals with arrays without duplicates else        this deals with arrays with duplicates   Is there any obvious function I m not thinking of  How to detect duplicate values in PHP array  has the right title  and is a very similar question  however if you actually read the question  he s looking for array count values

User · Answer

Php has an function to count the occurrences in the array http   www php net manual en function array-count-values php

User · Answer

Here s my take on this    after some benchmarking  I found this to be the fastest method for this   function has duplicates   array         return count  array keys  array flip   array           count   array           or depending on circumstances this could be marginally faster   function has duplicates   array          array   array count values   array        rsort   array        return  array 0   gt  1

User · Answer

I know you are not after array unique    However  you will not find a magical obvious function nor will writing one be faster than making use of the native functions   I propose   function array has dupes  array          streamline per  Felix    return count  array      count array unique  array        Adjust the second parameter of array unique   to meet your comparison needs

User · Answer

The simple solution but quite faster    elements   array merge range 1 10000000   1     function unique val inArray  arr         count   count  arr       foreach   arr as  i 1   gt   value            for  i 2    i 1   1   i 2  lt   count   i 2                  if  arr  i 2       arr  i 1                    return false                                    return true      time   microtime true   unique val inArray  elements   echo  This solution      microtime true  -  time    s   PHP EOL    Speed -  0 71

User · Answer

You can do it like that way also  This will return true if unique else return false    nofollow    count  modelIdArr      count array unique  modelIdArr      true   false

User · Answer

Find this useful solution  function get duplicates   array         return array unique  array diff assoc   array  array unique   array            After that count result if greater than 0 than duplicates else unique

User · Answer

PERFORMANCE SOLUTION    If you care about performance and micro-optimizations check this one-liner   function no dupes array  input array        return count  input array      count array flip  input array        Description   Function compares number of array elements in  input array with array flip ed elements  Values become keys and guess what - keys must be unique in associative arrays so not unique values are lost and final number of elements is lower than original   As said in manual array keys can be only type of int or string so this is what you can have in original array values to compare  otherwise PHP will start casting with unexpected results   PROOF FOR 10M RECORDS ARRAY   Most voted solution  14 187316179276s  Accepted solution  2 0736091136932s  This answer solution  0 14155888557434s  10   Test case    lt  php   elements   array merge range 1 10000000   1      time   microtime true   accepted solution  elements   echo  Accepted solution      microtime true  -  time    s   PHP EOL    time   microtime true   most voted solution  elements   echo  Most voted solution      microtime true  -  time    s   PHP EOL    time   microtime true   this answer solution  elements   echo  This answer solution      microtime true  -  time    s   PHP EOL   function accepted solution  array     dupe array   array     foreach  array as  val        sorry  but I had to add below line to remove millions of notices   if  isset  dupe array  val     dupe array  val  0     if    dupe array  val   gt  1      return true          return false     function most voted solution  array       return count  array      count array unique  array       function this answer solution array  input array        return count  input array      count array flip  input array        Notice that accepted solution might be faster in certain condition when not unique values are near the beginning of huge array

User · Answer

hasDuplicates   count  array   gt  count array unique  array       Will be true if duplicates  or false if no duplicates

User · Answer

Two ways to do it efficiently that I can think of    inserting all the values into some sort of hashtable and checking whether the value you re inserting is already in it expected O n  time and O n  space  sorting the array and then checking whether adjacent cells are equal  O nlogn  time and O 1  or O n  space depending on the sorting algorithm    stormdrain s solution would probably be O n 2   as would any solution which involves scanning the array for each element searching for a duplicate

User · Answer

I m using this   if count  array   count array count values  array         echo  all values are unique     else      echo  there s dupe values        I don t know if it s the fastest but works pretty good so far

User · Answer

You can do    function has dupes  array         dupe array   array        foreach   array as  val            if     dupe array  val   gt  1                return true                      return false

User · Answer

function hasDuplicate  array      d   array      foreach  array as  elements        if  isset  d  elements            d  elements    1       else        return true                return false

User · Answer

Keep it simple  silly      Simple OR logic      function checkDuplicatesInArray  array        duplicates FALSE      foreach  array as  k  gt  i           if  isset  value   i                  value   i  TRUE                    else               duplicates  TRUE                                return   duplicates       Regards

User · Answer

duplicate   false    if count array     count array unique array         duplicate   true

User · Answer

As you specifically said you didn t want to use array unique I m going to ignore the other answers despite the fact they re probably better   Why don t you use array count values   and then check if the resulting array has any value greater than 1

[php] php: check if an array has duplicates

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