dplm47571
dplm47571
2014-04-15 00:18

循环遍历数组并比较时间戳

I have two arrays that I like to loop through and compare the dates between each array.

$newArray = Array (
    [0] => Array (
            [id] => 1
            [date] => 26-11-2013 9:30:56 PM
        )
    [1] => Array (
            [id] => 2
            [date] => 30-11-2013 11:20:12 AM
        )
    [2] => Array (
            [id] => 3
            [date] => 26-11-2013 9:30:56 PM
        )
    [3] => Array (
            [id] => 4
            [date] => 30-11-2013 11:20:12 AM
        )
}

$oldArray = Array (
    [0] => Array (
            [id] => 1
            [date] => 26-11-2013 9:30:56 PM
        )
    [1] => Array (
            [id] => 2
            [date] => 26-11-2013 9:30:56 PM
        )
    [2] => Array (
            [id] => 3
            [date] => 26-11-2013 9:30:56 PM
        )
}

foreach ($newArray as $newPhoto) {
    foreach ($oldArray as $oldPhoto) {
        if (strtotime($newPhoto['date']) != strtotime($oldPhoto['date'])) {
            // download new photo
        }
    }
}

I realize that placing the foreach with a foreach is not going to cut it. What is the best way to loop through each of these arrays and compare the dates?

The $newArray has the latest photos and compares with the $oldArray if the timestamps do not match or there is a new one in the list, download the new images.

In the example, I would be downloading the second and fourth images and ignoring the others.

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3条回答

  • donh61500 donh61500 7年前

    I'd do it like this. It does not make any assumptions about the indices of either array, and will be still be fairly efficient as $oldArray grows in size.

    // index $oldArray by id for speed
    $index = array();
    foreach ($oldArray as $photo) {
        $index[$photo['id']] = $photo['date'];
    }
    
    // iterate through new photos, checking if each one needs downloading
    foreach ($newArray as $photo) {
        if (!isset($index[$photo['id']]) // photo is not in $oldArray
                || strtotime($photo['date']) > strtotime($index[$photo['id']])) { // photo is in $oldArray, but a new version is available
            // download new photo
        }
    }
    
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  • douchongbc72264 douchongbc72264 7年前

    Why use foreach, you can simply use for:

    for($i=0; $i<sizeof($newArray); $i++){
        if(strtotime($newArray[$i]['date']) != strtotime($oldArray[$i]['date'])){
            //new photo do sth
        }else {
            //old photo do sth or not :)
        }
    }
    
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  • dream07769 dream07769 7年前
    foreach ($newArray as $key => $newPhoto) {
        //If the key doesn't exist in $oldArray it is new
        if(!isset($oldArray[$key])){
          //download new photo
        }
        elseif (strtotime($newPhoto['date']) != strtotime($oldArray[$key]['date'])) { //timestamp mismatch
          //download new photo
        }
    }
    

    Note: I assume that your oldArray and newArray are keyed the same. I.e if id 1 is in the 0 spot of newArray I assume that id 1 is in the 0 spot in oldArray.

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