DIFFICULT Anonymous Function. Plz Help!!!!

[bradgrafelman]

Two items from the array that usort() is sorting.

[Paul_help_]

so to begin with,, $a is equal to the word 'but' and $b is equal to the word 'think' (because they are the 1st 2 words in the paragraph?? and then after comparing the first to words they move onto comparing 'not' and 'that'? and so on?

[bradgrafelman]

You could add print statements to the comparator function to see the elements passed to it in each call. For example, see this user comment on the usort() manual page.

[Paul_help_]

but am i correct in the comment i made just above above?

[bradgrafelman]

Paul help!;11032375 wrote:

but am i correct in the comment i made just above above?

No, because of the algorithm PHP uses to sort the array.

Using code similar to what was posted in the user comment above, the first few comparisons I see being made are:

a (is) is shorter than b (think), moving b down array
b (is) is shorter than a (Labrador), moving b up array
b (is) is shorter than a (coast), moving b up array
b (is) is shorter than a (the), moving b up array
b (is) is shorter than a (condition), moving b up array
b (is) is shorter than a (howling), moving b up array
a (as) is same length as b (is), keeping the same

[Paul_help_]

thanks. this makes better sense now.

[Paul_help_]

This algorithm that you speak of. Is that the algorithm of the usort() function?

[Weedpacket]

Yes; it's an implementation of quicksort.

[Paul_help_]

Hi guys.

There is just one little thing i can't understand about this code.

Basically, the above extract of code is from a book i am reading. And in the book it states:

In this case, the comparison function needs to determine if the length of the string $a is less than, equal
to, or greater than the length of the string $b . It can do this simply by subtracting the length of $a from
the length of $b and returning the result. (Remember from Chapter 5 that PHP ’ s strlen() function
returns the length of a string.)
Here, then, is the complete line of code to sort the array:
usort( $words, create_function( ‘$a, $b’, ‘return strlen($a) - strlen($b);’ ) );

I now understand virtually all of this code. The only thing i don't understand is how, in the book i am reading, it says:

subtracting the length of $a from the length of $b

now, to me, it looks like it is the other way around: $a - $b.

Am I missing something here?

Paul.

[NogDog]

Paul help!;11049443 wrote:

...

now, to me, it looks like it is the other way around: $a - $b.

Am I missing something here?

Paul.

Frankly, I never remember, so on the rare occasions when I need to do something like that, I try it one way with a small set of test data, and if it comes out in the wrong order, then I swap the 2 variables. 🙂

[laserlight]

Paul help! wrote:

now, to me, it looks like it is the other way around: $a - $b.

Am I missing something here?

NogDog wrote:

Frankly, I never remember, so on the rare occasions when I need to do something like that, I try it one way with a small set of test data, and if it comes out in the wrong order, then I swap the 2 variables.

I find it easy to remember by recalling how such a function would be used: comparison with 0 such that foo($x, $y) COMPARISON 0 would mean that $x COMPARISON $y is true, e.g., foo($x, $y) < 0 means that $x is less than $y for whatever "less than" means according to foo.

So, if you want to do the subtraction trick with $a and $b, then it means that to correctly test for $a less than $b, you must make it such that foo($a, $b) < 0. Given $a = 0, $b = 1, it is easy to see that 0 - 1 == -1, so you would return $a - $b.

[Paul_help_]

I suppose what i am trying to ask you is - has the author of the book i am reading got his words mixed up?

because in the code i tested (below), it subtracts the length of variable $b from $a,,,, not $a from $b.

$a = "hello world";

$b = "hi";

echo strlen($a) - strlen($b); // outputs: 9

[laserlight]

Yes, the words were swapped though the code is correct.