I want to create a panel dataset from two waves of the World Bank Enterprise Surveys (One collected in 2019 and a follow up collected in 2020 after the Covid19 out break. After appending the second wave of the enterprise survey I have noticed that there are missing values/observations on the dataset from the second wave (follow-up survey). I have a categorical variable (a6a) and a continuous variable a6c having missing values/observations. Since they have the same id, I was expecting to have labels or values on the dots (.). For example
idstd a6a a6c
680991 small 5
680991 . .
680992 large 456
680992 . .
680993 small 5
680993 . .
680994 medium 56
680994 . .



I want the dataset to look like this:



idstd a6a a6c
680991 small 5
680991 small 5
680992 large 456
680992 large 456
680993 small 5
680993 small 5
680994 medium 56
680994 medium 56
This is how the original data looks after appending

part of the first wave

Array


part of the second wave


Array