What is the best way to delete an array of values from an array?

Question

I want to be able to easily and quickly delete an array of needles from a haystack array. In actual fact I have a comma separated list of numbers (though this is a string i know) that need to be deleted from a second comma separated list of number that I pull from a field in my sql database.

So I need -

$orig_needle_list = "3456,5678"; The haystack list is in a field in a mysql database and is "3456, 4567, 5678, 6789" - so I basically want to update this field to "4567,6789"

Q1. Should I retrieve the haystack list, convert both to arrays and iterate over them with a nested foreach cycle and array_splice any matched values?

Q2 Can I use in_array to be faster than nested foreach method?

Q3 is there a way to cut out the middle man and update the field by performing this in an sql query?

thanks

Why do you have data stored like this in the first place? It sounds like somewhere along the line, you or someone else broke the rules of normalization. — Peter Bailey
– Peter Bailey, Commented Sep 7, 2010 at 15:16

sled · Accepted Answer · 2010-09-07 15:20:21Z

5

you don't need to iterate over things, there's a function called array_diff:

http://www.php.net/manual/en/function.array-diff.php

So create 2 arrays of the comma separated list and use array_diff, the resulting array is the difference of these two.

Storing comma separated lists in a database isn't a good idea because it breaks normalization.

answered Sep 7, 2010 at 15:20

sled

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2 Comments

undefined Over a year ago

thanks - do you mean I shouldnt use a comma to separate values? in other fields I have used a semicolon. Is this ok?

sled Over a year ago

the problem is not that you use commas or semicolons, the problem is you're storing multiple values in one database field (column) ! It'd be better to create an extra table with a foreign key to it's parent table to store the value. Look at en.wikipedia.org/wiki/Database_normalization You'll have many new rows in this new table but that's not a problem for your SQL server, indeed it speeds things up because it can index it. You could also perform this operation (array_diff) directly in the DB!

tamasd · Accepted Answer · 2010-09-07 15:19:28Z

0

I think you are looking for array_intersect() http://php.net/manual/en/function.array-intersect.php

answered Sep 7, 2010 at 15:19

tamasd

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Comments

andrewsi · Accepted Answer · 2012-11-13 05:07:08Z

0

try this:

implode(",",array_diff(explode(",",$haystack),explode(",",$orig_needle_list)));

edited Nov 13, 2012 at 5:07

andrewsi

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answered Sep 7, 2010 at 15:20

dweeves

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