error when looping with macros in the indexing

Question

I am trying to create a dummy variable to identify the next five observations after a selection of cutoffs. The first method in the code below works, but it looks a bit messy and I'd like to be able to adjust the number of observations I'm creating dummies for without typing out the same expression 30 times (usually a sign I'm doing something the hard way).

Every time I put a macro into the indexing, i.e.

[_n-`i']

I get the following error:

 _= invalid name
r(198);

I'd be very grateful for some advice.

sysuse auto.dta, replace
global cutoffs 3299 4424 5104 5788 10371

This works

sort price
gen A=0

foreach x in $cutoffs {
    replace A=1 if price==`x' 
    replace A=1 if price[_n-1]==`x'
    replace A=1 if price[_n-2]==`x'
    replace A=1 if price[_n-3]==`x'
    replace A=1 if price[_n-4]==`x'
    replace A=1 if price[_n-5]==`x'
}

This doesn't.

foreach x in $cutoffs {
    forval `i' = 0/25 { 
        replace A=1 if price[_n-`i']==`x'
    }
}

Any advice as to why?

Nick Cox Nick Cox · Accepted Answer · 2016-08-08T14:51:02

In Stata terms no loops are needed here at all, except those tacit in generate and replace. You want to set a counter going each time immediately after you hit a cutoff, and then identify counter values between 1 and 5. Here's some technique:

sysuse auto.dta, clear 
global cutoffs 3299,4424,5104,5788,10371
sort price 

gen counter = 0 if inlist(price, $cutoffs) 
replace counter = counter[_n-1] + 1 if missing(counter) 
gen wanted = inrange(counter, 1, 5) 

list price counter wanted 

     +---------------------------+
     |  price   counter   wanted |
     |---------------------------|
  1. |  3,291         .        0 |
  2. |  3,299         0        0 |
  3. |  3,667         1        1 |
  4. |  3,748         2        1 |
  5. |  3,798         3        1 |
     |---------------------------|
  6. |  3,799         4        1 |
  7. |  3,829         5        1 |
  8. |  3,895         6        0 |
  9. |  3,955         7        0 |
 10. |  3,984         8        0 |
     |---------------------------|
 11. |  3,995         9        0 |
 12. |  4,010        10        0 |
 13. |  4,060        11        0 |
 14. |  4,082        12        0 |
 15. |  4,099        13        0 |
     |---------------------------|
 16. |  4,172        14        0 |
 17. |  4,181        15        0 |
 18. |  4,187        16        0 |
 19. |  4,195        17        0 |
 20. |  4,296        18        0 |
     |---------------------------|
 21. |  4,389        19        0 |
 22. |  4,424         0        0 |
 23. |  4,425         1        1 |
 24. |  4,453         2        1 |
 25. |  4,482         3        1 |
     |---------------------------|
 26. |  4,499         4        1 |
 27. |  4,504         5        1 |
 28. |  4,516         6        0 |
 29. |  4,589         7        0 |
 30. |  4,647         8        0 |
     |---------------------------|
 31. |  4,697         9        0 |
 32. |  4,723        10        0 |
 33. |  4,733        11        0 |
 34. |  4,749        12        0 |
 35. |  4,816        13        0 |
     |---------------------------|
 36. |  4,890        14        0 |
 37. |  4,934        15        0 |
 38. |  5,079        16        0 |
 39. |  5,104         0        0 |
 40. |  5,172         1        1 |
     |---------------------------|
 41. |  5,189         2        1 |
 42. |  5,222         3        1 |
 43. |  5,379         4        1 |
 44. |  5,397         5        1 |
 45. |  5,705         6        0 |
     |---------------------------|
 46. |  5,719         7        0 |
 47. |  5,788         0        0 |
 48. |  5,798         1        1 |
 49. |  5,799         2        1 |
 50. |  5,886         3        1 |
     |---------------------------|
 51. |  5,899         4        1 |
 52. |  6,165         5        1 |
 53. |  6,229         6        0 |
 54. |  6,295         7        0 |
 55. |  6,303         8        0 |
     |---------------------------|
 56. |  6,342         9        0 |
 57. |  6,486        10        0 |
 58. |  6,850        11        0 |
 59. |  7,140        12        0 |
 60. |  7,827        13        0 |
     |---------------------------|
 61. |  8,129        14        0 |
 62. |  8,814        15        0 |
 63. |  9,690        16        0 |
 64. |  9,735        17        0 |
 65. | 10,371         0        0 |
     |---------------------------|
 66. | 10,372         1        1 |
 67. | 11,385         2        1 |
 68. | 11,497         3        1 |
 69. | 11,995         4        1 |
 70. | 12,990         5        1 |
     |---------------------------|
 71. | 13,466         6        0 |
 72. | 13,594         7        0 |
 73. | 14,500         8        0 |
 74. | 15,906         9        0 |
     +---------------------------+

In fact, your text says "the next five observations after" but your code implements not that only that, but the cutoff observation too. For the latter, use inrange(counter, 0, 5).

Understanding the principles explained here is crucial for this question.

For inrange() and inlist() see their help entries and/or this paper.

So, what did you do wrong?

This line

 forval `i' = 0/25 {

in illegal unless you have previously defined the local macro i (and rather odd style even then). You perhaps meant

 forval i = 0/25 {

although where the 25 comes from, given your problem statement, is unclear to me. The error message isn't especially helpful, but Stata is struggling to make sense of code with a hole in it, given that the local macro implied by your code is not defined.

error when looping with macros in the indexing

1 Answers