st: numbering observations

[Simon Moore <simoncmoore@gmail.com>]

I have data of the form:

date		dw		incid
6/may/00	friday		5
7/may/00	saturday	9
13/may/00	friday		10
14/may/00	saturday	12

dw is day of week and incid is the number of violent incidents recorded 
in police stats.

I wanted to collapse by weekend (here assuming a weekend is a Friday and 
Saturday) and therefore added in the following id (count):

gen count = 0

local cntr = 1
forval i = 1(2)`=_N' {
qui replace count = `cntr' in `i'
local cntr = `cntr' + 1
}
local cntr = 1
forval i = 2(2)`=_N' {
qui replace count = `cntr' in `i'
local cntr = `cntr' + 1
}

which gives:

date		dw		incid	count
6/may/00	friday		5	1
7/may/00	saturday	9	1
13/may/00	friday		10	2
14/may/00	saturday	12	2

and then:

collapse (sum) incid (min) date, by(count)

I have two questions.  First, I am certain I have seen a more elegant 
way of creating the count id posted on Statalist but searching has not 
revealed anything.  Is there one?

More importantly, if, for some reason, there is a missing saturday in 
the data (there isn't at the moment but it is a growing dataset) the 
collapse ..., by(count) will not work.  Is there an easier way of 
numbering successive weekends in Stata?

Regards

Simon Moore
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