Hello,
I have the following dataset for a number of countries.
I would like to generate an aggregate entry (call it africa under variable "country") which is a sum of all the values of the variable "ca" for all the countries by year.
I cannot figure out how to do it except doing it manually in Excel which is obviously not handy.
Can some help me:
Should I need to clarify my question, please let me know.

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input int year float index str87 country float ca
1980 15 "Algeria"                   61248.55
1981 15 "Algeria"                      63086
1982 15 "Algeria"                   67123.51
1983 15 "Algeria"                   70748.18
1984 15 "Algeria"                   74710.08
1985 15 "Algeria"                   77474.35
1986 15 "Algeria"                   77784.24
1987 15 "Algeria"                   77239.76
1988 15 "Algeria"                   76467.36
1989 15 "Algeria"                   79831.92
1980 39 "Benin"                      1860.74
1981 39 "Benin"                     1965.387
1982 39 "Benin"                     2177.307
1983 39 "Benin"                     2082.683
1984 39 "Benin"                     2247.842
1985 39 "Benin"                     2417.076
1986 39 "Benin"                     2469.006
1987 39 "Benin"                     2431.971
1988 39 "Benin"                     2505.768
1989 39 "Benin"                     2488.038
1980  1 "Botswana"                  1516.087
1981  1 "Botswana"                  1694.112
1982  1 "Botswana"                  1837.036
1983  1 "Botswana"                  2055.612
1984  1 "Botswana"                  2335.366
1985  1 "Botswana"                  2550.895
1986  1 "Botswana"                  2738.062
1987  1 "Botswana"                   2963.26
1988  1 "Botswana"                  3325.464
1989  1 "Botswana"                   4431.94
1980 14 "Burkina Faso"              2192.041
1981 14 "Burkina Faso"              2288.216
1982 14 "Burkina Faso"              2339.263
1983 14 "Burkina Faso"              2311.912
1984 14 "Burkina Faso"              2349.373
1985 14 "Burkina Faso"              2656.291
1986 14 "Burkina Faso"              2867.462
1987 14 "Burkina Faso"              2860.642
1988 14 "Burkina Faso"              3026.523
1989 14 "Burkina Faso"               3091.73
1980 30 "Burundi"                    1344.64
1981 30 "Burundi"                   1491.376
1982 30 "Burundi"                   1484.951
1983 30 "Burundi"                   1531.115
1984 30 "Burundi"                   1529.591
1985 30 "Burundi"                   1708.338
1986 30 "Burundi"                   1773.586
1987 30 "Burundi"                     1846.2
1988 30 "Burundi"                   1936.524
1989 30 "Burundi"                    1965.25
1980  2 "Cabo Verde"                 278.052
1981  2 "Cabo Verde"                 301.547
1982  2 "Cabo Verde"                 310.067
1983  2 "Cabo Verde"                  339.59
1984  2 "Cabo Verde"                 352.435
1985  2 "Cabo Verde"                 382.893
1986  2 "Cabo Verde"                 393.889
1987  2 "Cabo Verde"                  410.86
1988  2 "Cabo Verde"                 435.498
1989  2 "Cabo Verde"                 460.317
1980  3 "Cameroon"                 12794.186
1981  3 "Cameroon"                 13726.994
1982  3 "Cameroon"                 14749.424
1983  3 "Cameroon"                 15988.812
1984  3 "Cameroon"                 17275.252
1985  3 "Cameroon"                 17681.533
1986  3 "Cameroon"                 16752.086
1987  3 "Cameroon"                 15813.303
1988  3 "Cameroon"                 15216.575
1989  3 "Cameroon"                 14737.848
1980 35 "Central African Republic"   1490.16
1981 35 "Central African Republic"  1513.225
1982 35 "Central African Republic"  1540.405
1983 35 "Central African Republic"  1446.484
1984 35 "Central African Republic"  1550.996
1985 35 "Central African Republic"  1602.746
1986 35 "Central African Republic"  1660.092
1987 35 "Central African Republic"  1578.233
1988 35 "Central African Republic"  1611.128
1989 35 "Central African Republic"   1651.01
1980 31 "Comoros"                    421.845
1981 31 "Comoros"                    438.149
1982 31 "Comoros"                    466.119
1983 31 "Comoros"                    488.591
1984 31 "Comoros"                    508.673
1985 31 "Comoros"                    518.847
1986 31 "Comoros"                    529.224
1987 31 "Comoros"                    537.892
1988 31 "Comoros"                    552.348
1989 31 "Comoros"                    543.308
1980 16 "Congo"                     3243.096
1981 16 "Congo"                     3931.224
1982 16 "Congo"                     4857.743
1983 16 "Congo"                     5130.247
1984 16 "Congo"                     5500.578
1985 16 "Congo"                     5437.178
1986 16 "Congo"                     5062.998
1987 16 "Congo"                     5072.587
1988 16 "Congo"                     5162.182
1989 16 "Congo"                     5253.278
end