Help with code: generate variable with if statement

[carmen campagnolo]

Hi all,

I need to determine cumulative frequencies (in relative terms) for WTP (willingness to pay) variable.

I am using the following code but something is not right. I get error message that "if not found".

gen demand_oe = sum(c_oe) / $N if c_oe != .

This is what my data looks like

* Example generated by -dataex-. To install: ssc install dataex
clear
input int(id P_OE) float c_oe
 72 200  .
 42 200  .
302 200  .
 40 200  .
184 200  .
 78 199  2
349 199  2
192 175  3
 49 175  3
 45 175  3
272 155  1
370 150  9
149 150  9
317 150  9
 41 150  9
322 150  9
173 150  9
186 150  9
105 150  9
293 150  9
277 145  3
250 145  3
 53 145  3
 58 130  1
235 125  6
 64 125  6
139 125  6
152 125  6
111 125  6
315 125  6
342 120  5
167 120  5
171 120  5
221 120  5
166 120  5
176 115  1
368 110  5
183 110  5
 74 110  5
 54 110  5
206 110  5
236 109  1
242 105  2
329 105  2
351 100 16
163 100 16
337 100 16
231 100 16
 87 100 16
 39 100 16
 37 100 16
158 100 16
 30 100 16
 27 100 16
328 100 16
232 100 16
381 100 16
165 100 16
204 100 16
154 100 16
210  99  2
271  99  2
313  95  2
153  95  2
216  90  9
175  90  9
289  90  9
188  90  9
276  90  9
 36  90  9
279  90  9
269  90  9
115  90  9
164  85  5
 84  85  5
103  85  5
114  85  5
162  85  5
308  80 14
373  80 14
241  80 14
214  80 14
382  80 14
356  80 14
287  80 14
288  80 14
346  80 14
104  80 14
 28  80 14
319  80 14
350  80 14
197  80 14
281  79  2
256  79  2
109  75 12
145  75 12
156  75 12
 89  75 12
142  75 12
146  75 12
end

and this is how the c_oe was created:

** determine the frequencies for each level stated in the OE format

bysort P_OE: egen c_oe = count(P_OE) 




** only keep counts for the first observation per price level

replace c_oe = . if P_OE == P_OE[_N-1]




** descendingly sort WTP OE data

gsort - P_OE




** determine cumulative frequencies (in relative terms) for WTP in OE

gen demand_oe = sum(c_oe) / $N if c_oe != .

drop c_oe

Could someone highlight what I am doing wrong?

Any help is greatly appreciated.
Thanks

[Clyde Schechter]

Where does $N come from? You don't show any place where you defined it, and it is not a system global macro. If it is undefined, then Stata will interpret $N as an empty string. In that case your command reads as -gen demand_oe = sum(c_oe) / if c_oe != .- . And Stata, naturally, expects whatever follows / to be a variable. But there is no variable named if.