On Mon, 19 Sep 2011, Pietro Battiston wrote:
> I'd like to have some clarification on the line
>
> "b) that the new data carries clear observation information so that
> gretl can work out how to place the values"
>
> in the description of "append" from the Gretl Command reference.
By "observation information" gretl means the observation
markers in the first column (e.g. dates for time-series,
strings for indentifiable units such as countries).
> Basically, this is my situation: I have two databases. In both, I have a
> two fields "id1" and "id2". The combined fields are unique in the first
> database, while instead in the second I can have two different rows with
> the same "id1" and "id2" values.
>
> So, first question: when I append the second db to the first, are the
> common field names "clear observation information" for Gretl to do some
> sort of matching between the rows of the two databases?
No, gretl is not able to guess on that basis.
> Second question: the second database has a field "days", and my aim is
> that in my merged database, the (unique) row with given "id1" and "id2"
> has, in the field "days", the sum of the "days" variable in all rows
> with that combination of ids. How can I do that?
You should be able to do that sort of thing by loading the
data series into a matrix. For example, consider the following
simplified version of your data:
id1 id2 days
1 2 3
1 1 4
2 1 4
3 1 5
1 3 5
2 1 2
3 1 4
The script below will do what you describe, if I've understood
you correctly.
<hansl>
scalar imin = min(id1)
scalar imax = max(id1)
scalar jmin = min(id2)
scalar jmax = max(id2)
# count the number of ordered id pairs
scalar np = 0
loop i=imin..imax -q
loop j=jmin..jmax -q
if sum(id1 == i && id2 == j) > 0
np++
endif
endloop
endloop
printf "npairs = %d\n", np
matrix C = zeros(np, 3)
colnames(C, "id1 id2 days")
# cumulate the 'days' data for each ordered id pair
scalar r = 0
loop i=imin..imax -q
loop j=jmin..jmax -q
if sum(id1 == i && id2 == j) > 0
r++
C[r,1] = i
C[r,2] = j
loop k=1..$nobs -q
if id1[k] == i && id2[k] == j
C[r,3] += days[k]
endif
endloop
endif
endloop
endloop
print C
# write out as gretl data file
nulldata np --preserve
series id1 = C[,1]
series id2 = C[,2]
series days = C[,3]
store compacted.gdt id1 id2 days
</hansl>
Allin Cottrell
