Recall that Jon gave an example of data in wide form
"For example, say I have 5 years of data and the following information
for 5 observations:
ObsA 1 1 1 1 0
ObsB 1 1 1 0 0
ObsC 1 1 0 0 1
ObsD 1 0 1 1 1
ObsE 0 0 0 0 1
The variable names are something like yr1, yr2, yr3, yr4, yr5."
And is interested in spells of 1s and 0s. We are thus looking for spells
rowwise.
A better approach than my last suggestion would be based on collapsing
each row to its
pattern, defined in the following way:
1 1 1 1 1 is a pattern "1"
0 0 0 0 0 is a pattern "0"
A and B above are examples of pattern "10", etc.
This would be done with a loop:
gen pattern = ""
qui forval i = 1/5 {
replace pattern = pattern + string(yr`i') if string(yr`i') !=
substr(pattern, -1, 1)
}
substr(pattern, -1, 1) is the last character of -pattern-. Notice that
all works well when
the loop starts, as substr("", -1, 1) is empty and so string(yr1) will
certainly differ from
that.
With this reduction Jon can just select observations with a pattern of
"10".
Nick
[email protected]
Nick Cox
gen lastpos = .
quietly forval i = 1/5 {
replace lastpos = `i' if yr`i' == 1
}
You can also collapse each string to its positive occurrences.
gen signature = ""
forval i = 1/5 {
replace signature = signature + "`i'" if yr`i' == 1
}
The last positive is then the last character of that signature.
However, this is awkward whenever there are all zeros.
Jon Schwabish
Sergiy & Nick,
Thanks for your responses; they were both very
helpful. And yes, Nick is correct, Observation A does
not follow the criterion I laid out. Nonetheless....
I was wondering if you might have some thoughts on a
follow-up question. How would you go about identifying
the *last* non-zero observation in the series? In
other words, a series of numbers such as "111000", how
would you identify the third number in the sequence
(or even the fourth as the *first* zero observation).
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