Filling missing observations with equal parts of the existing observation (Stata) - stata

Question

I would like to fill the missing observation(s) with the values of the next cell and distribute it equally over the missing rows.
For example using data from below, I would fill value for 2004m1 and 2004m2 with 142 and also replace value for 2004m3 with 142, as we fill two missings (142 = 426/3). For 2005m7/m8 it would be 171 etc. I am able to fill the missings with revered sorting and carryforward, however I cannot figure out how to redistribute the values, especially that the number of rows that I try to fill can vary and it is not simple [_n+1].
My try to fill the values (but this does not redistribute):
carryforward value, gen(value_filled)
Example data set:
date_m value
2005m12 56
2005m11 150
2005m10 190
2005m9 157
2005m8 342
2005m7 .
2005m6 181
2005m5 151
2005m4 107
2005m3 131
2005m2 247
2005m1 100
2004m12 77
2004m11 181
2004m10 132
2004m9 153
2004m8 380
2004m7 .
2004m6 174
2004m5 178
2004m4 104
2004m3 426
2004m2 .
2004m1 .
Expected result
date_m value
2005m12 56
2005m11 150
2005m10 190
2005m9 157
2005m8 171
2005m7 171
2005m6 181
2005m5 151
2005m4 107
2005m3 131
2005m2 247
2005m1 100
2004m12 77
2004m11 181
2004m10 132
2004m9 153
2004m8 190
2004m7 190
2004m6 174
2004m5 178
2004m4 104
2004m3 142
2004m2 142
2004m1 142

Answer 1

Thanks for your data example, which is helpful, but as detailed in the Stata tag wiki and on Statalist an example using dataex is even better. Date and time variables are especially awkward otherwise.
You allude to carryforward, which is from SSC and which many have found useful. Having written the FAQ on this accessible here my prejudice is that most such problems yield quickly and directly to sorting, subscripting and replace. Your problem is trickier than most in including a value to be divided after an unpredictable gap of missing values.
This works for your example and doesn't rule out a simpler solution.
* Example generated by -dataex-. To install: ssc install dataex
clear
input float date int mvalue
551 56
550 150
549 190
548 157
547 342
546 .
545 181
544 151
543 107
542 131
541 247
540 100
539 77
538 181
537 132
536 153
535 380
534 .
533 174
532 178
531 104
530 426
529 .
528 .
end
format %tm date
gsort -date
gen copy = mvalue
replace copy = copy[_n-1] if missing(copy)
gen gap = missing(mvalue[_n+1]) | missing(mvalue)
replace gap = gap + gap[_n-1] if gap == 1 & _n > 1
sort date
replace gap = gap[_n-1] if inrange(gap[_n-1], 1, .) & gap >= 1
gen wanted = cond(gap, copy/gap, copy)
list , sepby(gap)
+----------------------------------------+
| date mvalue copy gap wanted |
|----------------------------------------|
1. | 2004m1 . 426 3 142 |
2. | 2004m2 . 426 3 142 |
3. | 2004m3 426 426 3 142 |
|----------------------------------------|
4. | 2004m4 104 104 0 104 |
5. | 2004m5 178 178 0 178 |
6. | 2004m6 174 174 0 174 |
|----------------------------------------|
7. | 2004m7 . 380 2 190 |
8. | 2004m8 380 380 2 190 |
|----------------------------------------|
9. | 2004m9 153 153 0 153 |
10. | 2004m10 132 132 0 132 |
11. | 2004m11 181 181 0 181 |
12. | 2004m12 77 77 0 77 |
13. | 2005m1 100 100 0 100 |
14. | 2005m2 247 247 0 247 |
15. | 2005m3 131 131 0 131 |
16. | 2005m4 107 107 0 107 |
17. | 2005m5 151 151 0 151 |
18. | 2005m6 181 181 0 181 |
|----------------------------------------|
19. | 2005m7 . 342 2 171 |
20. | 2005m8 342 342 2 171 |
|----------------------------------------|
21. | 2005m9 157 157 0 157 |
22. | 2005m10 190 190 0 190 |
23. | 2005m11 150 150 0 150 |
24. | 2005m12 56 56 0 56 |
+----------------------------------------+