Most efficient manner of handling this comparison?

schwim2

Hi there everyone!

I've already gotten some help from you for another part of my VIN decryption script but I'm stuck again on comparing a alphanum string to a range.

To explain better, Here's how you determine the age of your 73-79 Bronco:

Q00001 - S60000 = 1973
S60001 - V20000 = 1974
V20001 - X40000 = 1975
A00001 - D25000 = 1976
000001 - 099999 = 1977
X80001 - Z25000 = 1977
AE0001 - CK9999 = 1978
DC0001 - FK9000 = 1979

So the string I need to compare to retrieve the date could have 1 letter and 5 numbers, 2 letters and 4 numbers, or no letters and six numbers.

EA2601 would be a 79, 37630 would be a 77 as would a Y37668 and R87283 would be a 73.

My issue is that I simply can not think of an "efficient" way to handle this but maybe that's because there isn't one. The only solution I can think of is to first check whether character one and two is a letter or number, then do an if statement for every range until I've found a match.

Is that about the best I can hope for or is there something I'm not thinking of? I thought I'd ask before I began the function.

Thanks for your time!

Weedpacket

It looks like a series of [man]strcmp[/man] calls to find which range your VIN lies within would be enough.

schwim2

Hi there Weedpacket and thanks very much for your help!

I've never used this function before and it looks pretty nifty but I'm having an issue figuring out how to properly using it after reading the man page.

I used the following and tested it with a bunch of different examples within different ranges to see how it would behave, so I could figure out what to check for in my if statements but the results change so much in the appropriate range that I can't quite figure out what I'm looking for it to do. I tried smallest/smallest, adding the two together and picking the smallest and looking for the single smallest number to have it act as the closest, but each method failed with one test or another. Here's my test:

	$vindate = "EL4882";

echo strcmp($vindate, "Q00001").' | '.strcmp($vindate, "S60000").'<br>';
echo strcmp($vindate, "S60001").' | '.strcmp($vindate, "V20000").'<br>';
echo strcmp($vindate, "V20001").' | '.strcmp($vindate, "X40000").'<br>';
echo strcmp($vindate, "A00001").' | '.strcmp($vindate, "D25000").'<br>';
echo strcmp($vindate, "000001").' | '.strcmp($vindate, "099999").'<br>';
echo strcmp($vindate, "X80001").' | '.strcmp($vindate, "Z25000").'<br>';
echo strcmp($vindate, "AE0001").' | '.strcmp($vindate, "CK9999").'<br>';
echo strcmp($vindate, "DC0001").' | '.strcmp($vindate, "FK9000").'<br>';

Am I implementing it incorrectly or am I perhaps expecting something inappropriate from the result?

Weedpacket

If a string lies in the range between two other strings, then it will be greater than the string at the start of the range and less than the string at the end of the range. "A" < "B" and "B" < "C", hence "B" lies between "A" and "C".

schwim2

That doesn't seem to be an exclusive condition, however. If I try the following:

	$vindate = "BG2873";

echo strcmp($vindate, "Q00001").' | '.strcmp($vindate, "S60000").'<br>';
echo strcmp($vindate, "S60001").' | '.strcmp($vindate, "V20000").'<br>';
echo strcmp($vindate, "V20001").' | '.strcmp($vindate, "X40000").'<br>';
echo strcmp($vindate, "A00001").' | '.strcmp($vindate, "D25000").'<br>';
echo strcmp($vindate, "000001").' | '.strcmp($vindate, "099999").'<br>';
echo strcmp($vindate, "X80001").' | '.strcmp($vindate, "Z25000").'<br>';
echo strcmp($vindate, "AE0001").' | '.strcmp($vindate, "CK9999").'<br>';
echo strcmp($vindate, "DC0001").' | '.strcmp($vindate, "FK9000").'<br>';

I expect the second to last check to be the one that it falls in between, however, it falls in between two actually, the fourth condition also showing a gap between positive and negative:

-15 | -17
-17 | -20
-20 | -22
1 | -2
18 | 18
-22 | -24
1 | -1
-2 | -4

I do notice, however that the proper match is closer to zero(1 | -1 vs. 1 | -2). So does that mean I should find the one in between the smallest negative and positive number?

I'm sorry for my density. The man page makes it seem very simple:

Returns < 0 if str1 is less than str2; > 0 if str1 is greater than str2, and 0 if they are equal.

but I'm just not grasping it in practice.

Weedpacket

The magnitude is irrelevant. All that matters is the sign: whether the number is less than, greater than, or equal to zero.

In your example, there are only two cases where the test string is greater than one end of the range but less than the other. Of those two, only one has the same number of letters in its strings.

schwim2

Ok, so I need to also determine the number of letters in the strings as well. That makes sense. This is what I've come up with so far:

$vdchar = str_split($vindate);

$alpha = 0;
foreach($vdchar AS $vd){
	if(ctype_alpha($vd)){
		$alpha = ++$alpha;
	}
}

if($alpha == 2){
	/* Vindate contains two alpha chars */
	if(strcmp($vindate, "AE0001") >= 0 AND strcmp($vindate, "CK9999") <= 0){
		$year = '1978';
	}elseif(strcmp($vindate, "DC0001") >= 0 AND strcmp($vindate, "FK9000") <= 0){
		$year = '1979';
	};
}elseif($alpha == 1){
	/* Vindate contains one alpha chars */
	if(strcmp($vindate, "Q00001") >= 0 AND strcmp($vindate, "S60000") <= 0){
		$year = '1973';
	}elseif(strcmp($vindate, "S60001") >= 0 AND strcmp($vindate, "V20000") <= 0){
		$year = '1974';
	}elseif(strcmp($vindate, "V20001") >= 0 AND strcmp($vindate, "X40000") <= 0){
		$year = '1975';
	}elseif(strcmp($vindate, "A00001") >= 0 AND strcmp($vindate, "D25000") <= 0){
		$year = '1976';
	}elseif(strcmp($vindate, "X80001") >= 0 AND strcmp($vindate, "Z25000") <= 0){
		$year = '1977';
	};
}else{
	/* Vindate contains no alpha chars because we checked at the beginning of the process to make sure all is alphanumeric. */
	if(strcmp($vindate, "000001") >= 0 AND strcmp($vindate, "099999") <= 0){
		$year = '1977';
	};

	if(!ISSET($year)){
		UNSET($matchfound);
	}
}

I'll do some testing and see if I've managed to muddle into the solution 🙂