Thank you jakub and Hack-R! Yes, these are my actual data. The data I am starting from are the following:
[A] #first, longer dataset
CODE_t2 VALUE_t2
111 3641
112 1691
121 1271
122 185
123 522
124 0
131 0
132 0
133 0
141 626
142 170
211 0
212 0
213 0
221 0
222 0
223 0
231 95
241 0
242 0
243 0
244 0
311 129
312 1214
313 0
321 0
322 0
323 565
324 0
331 0
332 0
333 0
334 0
335 0
411 0
412 0
421 0
422 0
423 0
511 6
512 0
521 0
522 0
523 87
In the above table, we can see the 44 land use CODES (which I inappropriately named "class" in my first entry) for a certain city. Some values are just 0, meaning that there are no land uses of that type in that city. Starting from this table, which displays all the land use types for t2 and their corresponding values ("VALUE_t2") I have to reconstruct the previous amount of land uses ("VALUE_t1") per each type.
To do so, I have to add and subtract the value per each land use (if not 0) by using the "change land use table" from t2 to t1, which is the following:
[B] #second, shorter dataset
CODE_t2 CODE_t1 VALUE_CHANGE1
121 112 2
121 133 12
121 323 0
121 511 3
121 523 2
123 523 4
133 123 3
133 523 4
141 231 12
141 511 37
So, in order to get VALUE_t1 from VALUE_t2, I have, for instance, to subtract 2 + 12 + 0 + 3 + 2 hectares (first 5 values of the second, shorter table) from the value of land use type/code 121 of the first, longer table (1271 ha), and add 2 hectares to land type 112, 12 hectares to land type 133, 3 hectares to land type 511 and 2 hectares to land type 523. And I have to do that for all the land use types different than 0, and later also from t1 to t0.
What I have to do is a sort of loop that would both add and subtract, per each land use type/code, the values from VALUE_t2 to VALUE_t1, and from VALUE_t1 to VALUE_t0.
Once I estimated VALUE_t1 and VALUE_t0, I will put the values in a simple table showing the relative variation (here the values are not real):
CODE VALUE_t0 VALUE_t2 % VAR t2-t0
code1 50 100 ((100-50)/50)*100
code2 70 80 ((80-70)/70)*100
code3 45 34 ((34-45)/45)*100
What I could do so far is:
land_code <- names(A)[-1]
land_code
A$VALUE_t1 <- for(code in land_code{
cbind(A[1], A[land_code] - B[match(A$CODE_t2, B$CODE_t2), land_code])
}
If I use the loop I get an error, while if I take it away:
A$VALUE_t1 <- cbind(A[1], A[land_code] - B[match(A$CODE_t2, B$CODE_t2), land_code])
it works but I don't really get what I want to get... so far I was working on how to get a new column which would contain the new "add & subtract" values, but haven't succeeded yet. So I worked on how to get a new column which would at least match the land use types first, to then include the "add and subtract" formula.
Another problem is that, by using "match", I get a shorter A$VALUE_t1 table (13 rows instead of 44), while I would like to keep all the land use types in dataset A, because I will have then to match it with the table including VALUES_t0 (which I haven't shown here).
Sorry that I cannot do better than this at the moment... and I hope to have explained better what I have to do. I am extremely grateful for any help you can provide to me.
thanks a lot
