Using dif function followed by a where statement

[Roy]

Hi guys,

First of all my apologies if this question is simple, but it was hard to search for similar questions.

I have a dataset like this:

a	b	count	dif
6		6	6
19		19	13
	32	32	13
91		91	59
105		105	14
	143	143	38
		144	1
172		172	28
	199	199	27
	272	272	42
326		326	54
356		356	30

Column count equals either a or b, whichever is not missing; while dif is simply the difference between each observation in count and its lag value. My desired output is this:

a	b	count	dif
6		6	6
19		19	13
91		91	59
105		105	14
172		172	28
326		326	54
356		356	30

This is to say, I want to keep only observations where a is not missing, while keeping dif value as it was. But once I use where a ne .; the new dif adjusts itself automatically (e.g. row 3 becomes 72 rather than 59). Any suggestions would be greatly appreciated.

Cheers

Roy

[Roy]

Hi guys,

Please ignore this question. I just realised I can put the where statement in a separate procedure to make it work. Thanks.

Roy