How to fill in observations using other observations R or Stata

Question

I have a dataset like this:

ID dum1 dum2 dum3 var1
1  0    1    .    hi
1  0    .    0    hi
2  1    .    .    bye
2  0    0    1    .

What I'm trying to do is that I want to fill in information based on the same ID if observations are missing. So my end product would be something like:

ID dum1 dum2 dum3 var1
1  0    1    0    hi
1  0    1    0    hi
2  1    0    1    bye
2  0    0    1    bye

Is there any way I can do this in R or Stata?

Answer 1

This continues discussion of Stata solutions. The solution by @Pearly Spencer looks backward and forward from observations with missing values and so is fine for the example with just two observations per group, and possibly fine for some other situations.

An alternative approach makes use, as appropriate, of the community-contributed commands mipolate and stripolate from SSC as explained also at https://www.statalist.org/forums/forum/general-stata-discussion/general/1308786-mipolate-now-available-from-ssc-new-program-for-interpolation

Examples first, then commentary:

clear

input ID dum1a dum2a dum3a str3 var1a
1  0    1    .    "hi"
1  0    .    0    "hi"
2  1    .    .    "bye"
2  0    0    1    ""
2  0    1    .    "" 
end

gen long obsno = _n 

foreach v of var dum*a { 
    quietly count if missing(`v') 
    if r(N) > 0 capture noisily mipolate `v' obsno, groupwise by(ID) generate(`v'_2) 
}

foreach v of var var*a { 
    quietly count if missing(`v') 
    if r(N) > 0 capture noisily stripolate `v' obsno, groupwise by(ID) generate(`v'_2) 
} 

list 

     +----------------------------------------------------------------+
     | ID   dum1a   dum2a   dum3a   var1a   obsno   dum3a_2   var1a_2 |
     |----------------------------------------------------------------|
  1. |  1       0       1       .      hi       1         0        hi |
  2. |  1       0       .       0      hi       2         0        hi |
  3. |  2       1       .       .     bye       3         1       bye |
  4. |  2       0       0       1               4         1       bye |
  5. |  2       0       1       .               5         1       bye |
     +----------------------------------------------------------------+

Notes:

1. The groupwise option of mipolate and stripolate uses the rule: replace missing values within groups with the non-missing value in that group if and only if there is only one distinct non-missing value in that group. Thus if the non-missing values in a group are all 1, or all 42, or whatever it is, then interpolation uses 1 or 42 or whatever it is. If the non-missing values in a group are 0 and 1, then no go.

2. The variable obsno created here plays no role in that interpolation and is needed solely to match the general syntax of mipolate.

3. There is no assumption here that groups consist of just two observations or have the same number of observations. A common playground for these problems is data on families whenever some variables were recorded only for certain family members but it is desired to spread the values recorded to other family members. Naturally, in real data families often have more than two members and the number of family members will vary.

4. This question exposed a small bug in mipolate, groupwise and stripolate, groupwise: it doesn't exit as appropriate if there is nothing to do, as in dum1a where there are no missing values. In the code above, this is trapped by asking for interpolation if and only if missing values are counted. At some future date, the bug will be fixed and the code in this answer simplified accordingly, or so I intend as program author.

5. mipolate, groupwise and stripolate, groupwise both exit with an error message if any group is found with two or more distinct non-missing values; no interpolation is then done for any groups, even if some groups are fine. That is the point of the code capture noisily: the error message for dum2a is not echoed above. As program author I am thinking of adding an option whereby such groups will be ignored but that interpolation will take place for groups with just one distinct non-missing value.