When declaring an Array in PHP, the index's may be created out of order...I.e
Array[1] = 1
Array[19] = 2
Array[4] = 3
My question. In creating an array like this, is the length 19 with nulls in between? If I attempted to get Array[3] would it come as undefined or throw an error? Also, how does this affect memory. Would the memory of 3 index's be taken up or 19?
Also currently a developer wrote a script with 3 arrays FailedUpdates[] FailedDeletes[] FailedInserts[]
Is it more efficient to do it this way, or do it in the case of an associative array controlling several sub arrays
"Failures" array(){
["Updates"] => array(){
[0] => 12
[1] => 41
}
["Deletes"] => array(){
[0] => 122
[1] => 414
[1] => 43
}
["Inserts"] => array(){
[0] => 12
}
}
Memory effiency isn't really something you need to worry about in PHP unless you're dealing with really huge arrays / huge numbers of variables.
An array in PHP isn't really like an array in C++ or a similar lower-level language; an array in PHP is a map. You have a list of keys (which must be unique and all of type string or integer), and a list of values corresponding to the keys. So the following is a legal array:
array(0 => 'butt', 1 => 'potato', 2 => 'tulip')
but so is
array(5 => 'i', 'barry' => 6, 19 => array(-1 => array(), 7 => 'smock'))
In both cases there are 3 entries in the array, hence 3 keys and 3 values.
In addition to the keys and values in the array, one array may be distinguished from another by the order in which the key/value pairs occur. If you define an array so that it has nonnegative integers as keys, this will often be the expected order. The order matters when you use constructs like foreach().
array[3] will be undefined/unset but not causing an error, and the array will use only memory for that 3 values - php isn't like C where you have to look at those things.
Accessing $arr[3] gives a notice: Notice: Undefined offset: 3 in /data/home/sjoerd/public_html/svnreps/test/a.php on line 3. You can avoid this by checking with isset() or array_key_exists().
There are no nulls stored.
Having empty elements won't take up extra memory.
Whether you should use multiple variables or an array depends on the context and how you use the variables.
Related
I want to check, if array A contains all the items from array B (may contain others, but must contain all), when both arrays are multidimensional, i.e. can contains different variable types.
I've seen a lot (particularly this, this, this, this, this and this, also this, this and this as well). I've read PHP doc. Everything, that I checked, fails with "Array to string conversion" notice. Especially wen using array_intersect() or array_diff().
I'm using strict error checking, so notices actually holds further execution of entire script and are something, I don't generally like and want to avoid. Is it possible in this case?
My array A is:
Array
(
[0] => content/manage/index
[Content] => Array
(
[title] =>
[type] => 5
[category] =>
[recommended] =>
[featured] =>
[status] =>
[views] =>
[last_access_date] =>
[creation_date] =>
[modification_date] =>
[availability_date] =>
[author_id] =>
)
)
My array B is:
Array
(
[0] => /content/manage/index
[Content] => Array
(
[type] => 1
)
)
So, is there any way I can if I can use array_intersect on multidimensional arrays containing different variable types without getting notice?
My problem (and question) came out of misunderstanding, what "Array to string conversion" notice really means. In my case, it was trying to tell me, that I'm trying to walk multidimensional array with functions designed to be used on single dimension array.
Understanding that led me to a solution within few seconds. There are many of them here, on SO, but the one given by deceze here looked the best for me. So I adopted it into the form of such function:
function recursiveArrayIntersect($array1, $array2)
{
$array1 = array_intersect_key($array1, $array2);
foreach($array1 as $key=>&$value)
{
if(is_array($value)) $value = recursiveArrayIntersect($value, $array2[$key]);
}
return $array1;
}
I adopted it to my project and my way of coding, but all the credits still goes to deceze (his answer here)!
Now I can find an intersection of virtually any array, no matter what kind of variable types it contain and no matter of, how deep it is (how many subarrays it contains).
I can't see to find an answer for this, but it's been bugging me for a while.
When using multidimensional arrays in php (or any language for that matter), do you get any efficiency and productivity out of saving an array of a multidimensional array as its separate array or accessing that "array" element directly from the whole array?
For example,
print_r($myArray);
Array
(
[2] => Array
(
[7.0] => Array
(
[0] => 1
[1] => 23
)
[16.0] => Array
(
[0] => 4
[1] => 28
)
)
[5] => Array
(
[17.0] => Array
(
[0] => 1
[1] => 3
)
)
)
If I needed to REPEATABLY access the array of [16.0], would it be better to just save that entry as its own array until I don't need it anymore, or is it better just to access it directly?
Option 1:
$tempArray=$myArray[2]["16.0"];
echo "Index=".$tempArray[0].";
or
Option 2:
echo "Index=".$myArray[2]["16.0"][0];
Of course this is just a tiny example, but if the values in (arbitrary) $array[.][.][n][...] are being accessed more than once, and the value of n depends on the index of a loop, is there any difference between accessing the element directly or saving that array (deep down on the layers of the array) as its own array and accessing its values that way?
If you look at the bytecode generated for these statements:
$tempArray=$myArray[2]["16.0"];
echo $tempArray[0];
FETCH_DIM_R $3 $myArray, 2
FETCH_DIM_R $4 $3, '16.0'
ASSIGN $tempArray, $4
FETCH_DIM_R $6 $tempArray, 0
ECHO $6
echo $myArray[2]["16.0"][0];
FETCH_DIM_R $7 $myArray, 2
FETCH_DIM_R $8 $7, '16.0'
FETCH_DIM_R $9 $8, 0
ECHO $9
(I've reformatted and removed the EXT_STMT markers). You can see that the only difference is the actual assignment to $tempArray. You might think that an array assignment is expensive. However PHP uses a referencing model and does a lazy copy-on-write, so it is not, and the cost is the pretty much same whatever the array size.
(Except of course if you change elements after the assignemt, so $tempArray is no longer the same as its originating slice, and at that point the memory usage jumps as the assign triggers the clone of the slice as the references need to be split.)
OK, this approach might be worthwhile if you are doing a lot of localised readonly access to a slice to save the repeated FETCH_DIM_R lookups (the PHP compile does absolutely no local optimisation of repeated use of indexes). However, the opportunities to shoot yourself in the foot on update are significant.
Why not benchmark this yourself using a loop and microtime() and memory_get_usage()?
You can easily test this yourself by creating an immense multidimensional array with a for loop, but accessing it directly will generally be faster when indexing large arrays.
With smaller arrays (~500 items or less) it isn't going to make a noticeable difference.
I have an array like
array (
(1) => array => ([1]=aa, [2]=other keys and values),
(2) => array => ([1]=bb, [2]=other keys and values),
(3) => array => ([1]=cc, [2]=other keys and values),
(4) => array => ([1]=aa, [2]=other keys and values),
(5) => array => ([1]=bb, [2]=other keys and values),
(6) => array => ([1]=cc, [2]=other keys and values),
(7) => array => ([1]=bb, [2]=other keys and values)
)
I would like to make arrays based on [1] = aa/bb/cc/dd.
To divide the original array in to various unique arrays which have same value of [1] key.
I do not want to use foreach as the result set is expected to reach 10k rows.
Is this optimal at all??
No matter what solution you choose, you will have to loop over all of the rows in your array, no matter what. Either directly or indirectly. There is no magic code that can decide what's inside a sealed box without opening the box.
So, apart from the obvious foreach you can use array_walk
Is this optimal at all??
Definitely not.
Though it is not foreach to blame but a programmer who have 10k rows to loop over.
If it's regular web-page served on user's request, there shouldn't be 10k rows by any means. You have to reduce the number at least by factor of 100. Or let the data storage to do the necessary calculations.
Is it more efficient to use the key intersect or the value intersect if both key and value have the same contents for example:
Array
(
[743] => 743
[744] => 744
[745] => 745
[746] => 746
[747] => 747
[748] => 748
)
Is there any difference in performance in using one or the other with the same values. Similar to the difference of using double or single quotes?
From another post: I have two unordered integer arrays, and i need to know how many integers these arrays have in common
Depending on your data (size) you
might want to use
array_intersect_key() instead of
array_intersect(). Apparently the
implementation of array_intersect
(testing php 5.3) does not use any
optimization/caching/whatsoever but
loops through the array and compares
the values one by one for each element
in array A. The hashtable lookup is
incredibly faster than that.
I'm using cakephp and am getting back a "double array" where it is giving me 2 arrays where it should be 1, I have looked into the issue as far as cakephp and can't figure it out and just want to move past this for now so I am wondering if anyone knows how to unset a second array if a variable has 2 arrays.. below is the print_r of the array, its just one variable that has this, which I find odd.. so I want to make it so there is not a 2nd set of duplicate values, if I do an array_push it pushes both values for that index into the resulting new array index so that won't work
one variable is equal to the following:
Array ( [0] => 42 [1] => 62 ) Array ( [0] => 42 [1] => 62 )
EDIT:
This is not an issue of my printing out the array twice accidentally, as I said above, with a foreach array_push of the variable, i end up with this, which is odd:
Array ( [0] => 4242 [1] => 6262 )
EDIT:
This is the cakephp database call that I am using, I know I didn't ask this in regards to cakephp but since some people think this is impossible i am posting this just so you can see what it does if you want
$specificfields_array = $this->Mymodel->find('list', array('fields' =>'Mymodel.id'),
'conditions' => array('emailgroup' => $categorynumber, 'sent' => '0');));
EDIT:
This is what a "foreach" array_push is:
$mynewarray = array();
foreach ($specificfields as $specificfields_current) {
array_push ($mynewarray, $specificfields_current);
}
A variable cannot "have two arrays". It can be one array that has two arrays nested. The scenario you describe is impossible (probably there are two print_r there or there is a < character hiding stuff – check the HTML source).
Can you post the controller, the model and the view file with your print_r calls to the http://bin.cakephp.org/ site and post the links back here so we can see all of your code?