Multi sorts on multidimensional array?

[Anon]

I am having trouble getting the proper results returned from a sort on a multidimentiaonl array. I am trying to sort the data by a specific column, then sort that new ordered data again by another column. For example, sort a members list by last name, and then by city.

The $members data looks like this [name], [tel], [city], [number] ...

Smith, 123 4567, Vancouver, 18
Jones, 123 5555, Seattle, 18
Adams, 555 1212, Vancouver, 20
James, 333 2345, Portland, 21
Watts, 454 7777, Vancouver, 19

... after sorting, it should look like this

Jones, 123 5555, Seattle, 18
James, 333 2345, Portland, 21
Adams, 555 1212, Vancouver, 20
Smith, 123 4567, Vancouver, 18
Watts, 454 7777, Vancouver, 19

Here is what I have tried.

Sort by name

function cmp_name($a,$b) {
if ($a[last] == $b[last]) return 0;
return ($a[name]<$b[name]) ? -1 : 1;
}

Sort by city

function cmp_city($a,$b) {
if ($a[city] == $b[city]) return 0;
return ($a[city]<$b[city]) ? -1 : 1;
}

Perform the 2 sorts

usort($member,"cmp_name");
usort($member,"cmp_city");

On there own each function works as I woud expect. However, when I call them one after the other, as shown above, the data is indeed sorted by city, BUT the names are not in alphebetical order.

I have also looked at the array_multisort function, but have yet been able to figure that beast out.

Any ideas would be most apreciated.

Thanks,
-Bob

[Anon]

Add a check in your cmp_city function if the cities are equal, ie

Sort by city

function cmp_city($a,$b) {
if ($a[city] == $b[city]) {
if ($a[name] == $b[name]) return 0;
return ($a[name]<$b[name]) ? -1 : 1;
}
return ($a[city]<$b[city]) ? -1 : 1;
}

When performing the sort there is no guarantee that the original order of items is preserved if the key you are sorting on is the same in both items.

[Anon]

Thanks BG,

That's the secret!
My sort now works perfectly.

-Bob