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POComparing multiple very large csv files against each other
 

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  1. POComparing multiple very large csv files against each other
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    <p>I have n csv files which I need to compare against each other and modify them afterwards. The Problem is that each csv file has around 800.000 lines.</p> <p>To read the csv file I use <em>fgetcsv</em> and it works good. Get some memory pikes but in the end it is fast enough. But if I try to compare the array against each other it takes ages.</p> <p>One other Problem is that I have to use a foreach to get the csv data with fgetcsv because of the n amount of files. I end up with one ultra big array and can't compare it with array_diff. So i need to compare it with nested foreach loops and that take ages.</p> <p>a code snippet for better understanding:</p> <pre><code>foreach( $files as $value ) { $data[] = $csv-&gt;read( $value['path'] ); } </code></pre> <p>my csv class use fgetcsv to add the output to the array:</p> <pre><code>fgetcsv( $this-&gt;_fh, $this-&gt;_lengthToRead, $this-&gt;_delimiter, $this-&gt;_enclosure ) </code></pre> <p>Every data of all the csv files are stored in the $data array. This is probably the first big mistake to use only one array, but I have no clue how to stay flexible with the files without to use an foreach. I tried to use flexible variable names but I stucked there as well :)</p> <p>Now I have this big array. Normally if I try to compare the values against each other and to find out if the data from file one exists in file two and so on, I use array_diff or array_intersect. But in this case I have only this one big array. And as I said, to run an foreach over it takes ages.</p> <p>Also after only 3 files I have an array with 3 * 800.000 entries. I guess latest after 10 files my memory will explode.</p> <p>So is there any better way to use PHP to compare n amount of very large csv files?</p>
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    1. USJoseph Silber
    1. USTalisin
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    1. CODoes it have to be PHP? Maybe there is a command-line utility that does this? How are you comparing the files exactly?
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      1. USPekka 웃
    2. COI am a programmer of the 1980' - then we solved it by using sort, then some logic to compare, then a third file with result. Some times you spilt the job in smaller chunks - and then run them serial. This is not a solution, but a way of thinking ...
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      1. USMike
    3. COwhat's the point in storing all files in one array?
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      1. USYour Common Sense
 

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