Dear all,

I am currently working with a country year panel dataset, which has the following variables for several items (e.g., rice, potatoes, millet) : production (in tonnes), production_value(million USD), producer price (prodprice, denoted by USD/tonne). Each country belongs to a particular region (countrygroup), e.g. AGO to Middle Africa, ALB to Southern Europe. See example below:

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input str3 iso3code int(year itemcode) str44 item double production float(production_value prodprice) str39 countrygroup
"AGO" 2010  27 "Rice, paddy"                     17697   7.52894  425.4 "Middle Africa"  
"AGO" 2010  56 "Maize"                         1072737  472.7219  440.7 "Middle Africa"  
"AGO" 2010  79 "Millet"                          40723 12.805456  314.5 "Middle Africa"  
"AGO" 2010  83 "Sorghum"                         46787 14.712298  314.5 "Middle Africa"  
"AGO" 2010 116 "Potatoes"                       841279  408.2558  485.3 "Middle Africa"  
"AGO" 2010 122 "Sweet potatoes"                 986563 284.46454  288.3 "Middle Africa"  
"AGO" 2010 125 "Cassava"                      13858681  4599.167  331.9 "Middle Africa"  
"AGO" 2010 176 "Beans, dry"                     250117   363.586 1453.7 "Middle Africa"  
"AGO" 2010 236 "Soybeans"                         6087  6.623092 1088.1 "Middle Africa"  
"AGO" 2010 242 "Groundnuts, with shell"         115164 119.66787 1039.1 "Middle Africa"  
"AGO" 2010 463 "Vegetables, fresh nes"          336716 135.01175  410.2 "Middle Africa"  
"AGO" 2010 486 "Bananas"                       2047955  356.5315  174.1 "Middle Africa"  
"AGO" 2010 574 "Pineapples"                     313365   308.913  985.8 "Middle Africa"  
"AGO" 2010 656 "Coffee, green"                    9951  5.088878  511.4 "Middle Africa"  
"AGO" 2011  27 "Rice, paddy"                     23209 10.253644  441.8 "Middle Africa"  
"AGO" 2011  56 "Maize"                         1262222  502.5521  398.1 "Middle Africa"  
"AGO" 2011  79 "Millet"                          61226 17.793945  290.6 "Middle Africa"  
"AGO" 2011  83 "Sorghum"                         62169 19.921137  320.4 "Middle Africa"  
"AGO" 2011 116 "Potatoes"                       841252  385.0954  457.8 "Middle Africa"  
"AGO" 2011 122 "Sweet potatoes"                1045104 287.04694  274.7 "Middle Africa"  
"AGO" 2011 125 "Cassava"                      14333509 4409.8525  307.7 "Middle Africa"  
"AGO" 2011 176 "Beans, dry"                     303521  476.2774 1569.2 "Middle Africa"  
"AGO" 2011 236 "Soybeans"                         7743  8.242956 1064.6 "Middle Africa"  
"AGO" 2011 242 "Groundnuts, with shell"         161116 158.65514  984.7 "Middle Africa"  
"AGO" 2011 463 "Vegetables, fresh nes"          343142 135.16719  401.3 "Middle Africa"  
"AGO" 2011 486 "Bananas"                       2646073 546.48376  206.5 "Middle Africa"  
"AGO" 2011 574 "Pineapples"                     326352 300.52188  920.9 "Middle Africa"  
"AGO" 2011 656 "Coffee, green"                   10192  7.161056  702.6 "Middle Africa"  
"AGO" 2012  27 "Rice, paddy"                     21492 15.218292  708.1 "Middle Africa"  
"AGO" 2012  56 "Maize"                          454343  315.0534  693.4 "Middle Africa"  
"AGO" 2012  79 "Millet"                          18379   6.87278  373.9 "Middle Africa"  
"AGO" 2012  83 "Sorghum"                         11491  4.670162  406.4 "Middle Africa"  
"AGO" 2012 116 "Potatoes"                       654160  450.1857  688.2 "Middle Africa"  
"AGO" 2012 122 "Sweet potatoes"                 644854 303.28442  470.3 "Middle Africa"  
"AGO" 2012 125 "Cassava"                      10636400 4445.3906  417.9 "Middle Africa"  
"AGO" 2012 176 "Beans, dry"                      96217 220.71828   2294 "Middle Africa"  
"AGO" 2012 236 "Soybeans"                         5898  7.351807 1246.5 "Middle Africa"  
"AGO" 2012 242 "Groundnuts, with shell"          66616  83.73406   1257 "Middle Africa"  
"AGO" 2012 463 "Vegetables, fresh nes"          360000 224.74557  624.3 "Middle Africa"  
"AGO" 2012 486 "Bananas"                       2991454 1504.0627  502.8 "Middle Africa"  
"AGO" 2012 574 "Pineapples"                     280906  41.19376  146.6 "Middle Africa"  
"AGO" 2013  27 "Rice, paddy"                     37608 16.170326    430 "Middle Africa"  
"AGO" 2013  56 "Maize"                         1548750  600.4482  387.7 "Middle Africa"  
"AGO" 2013  79 "Millet"                          38603  10.91878  282.8 "Middle Africa"  
"AGO" 2013  83 "Sorghum"                         46423  14.57839    314 "Middle Africa"  
"AGO" 2013 116 "Potatoes"                       670136 298.55328  445.5 "Middle Africa"  
"AGO" 2013 122 "Sweet potatoes"                1199749  321.3227  267.8 "Middle Africa"  
"AGO" 2013 125 "Cassava"                      16411674   4924.27    300 "Middle Africa"  
"AGO" 2013 176 "Beans, dry"                     311988  476.7179   1528 "Middle Africa"  
"AGO" 2013 236 "Soybeans"                        10326 10.698492 1036.1 "Middle Africa"  
"AGO" 2013 242 "Groundnuts, with shell"         192028 162.80493  847.8 "Middle Africa"  
"AGO" 2013 358 "Cabbages and other brassicas"   308763 138.67711  449.1 "Middle Africa"  
"AGO" 2013 388 "Tomatoes"                        17000  4.900004  288.2 "Middle Africa"  
"AGO" 2013 463 "Vegetables, fresh nes"          350000  84.56429  241.6 "Middle Africa"  
"AGO" 2013 486 "Bananas"                       3095013  919.9907  297.2 "Middle Africa"  
"AGO" 2013 574 "Pineapples"                     479357   335.536    700 "Middle Africa"  
"AGO" 2014  27 "Rice, paddy"                     42288  17.87684  422.2 "Middle Africa"  
"AGO" 2014  56 "Maize"                         1686869  650.0447  384.8 "Middle Africa"  
"AGO" 2014  79 "Millet"                          43056  10.83757  251.4 "Middle Africa"  
"AGO" 2014  83 "Sorghum"                         48133 14.861218  308.3 "Middle Africa"  
"AGO" 2014 116 "Potatoes"                       671468 283.85657  422.2 "Middle Africa"  
"AGO" 2014 122 "Sweet potatoes"                1928954  508.5243  263.3 "Middle Africa"  
"AGO" 2014 125 "Cassava"                       7638880 1789.7117    234 "Middle Africa"  
"AGO" 2014 176 "Beans, dry"                     401500  587.0212 1460.1 "Middle Africa"  
"AGO" 2014 236 "Soybeans"                        13763 14.019545 1017.3 "Middle Africa"  
"AGO" 2014 242 "Groundnuts, with shell"         252480 211.84665  837.9 "Middle Africa"  
"AGO" 2014 358 "Cabbages and other brassicas"   335467 148.13731    441 "Middle Africa"  
"AGO" 2014 388 "Tomatoes"                        16295  4.498381  274.7 "Middle Africa"  
"AGO" 2014 463 "Vegetables, fresh nes"          348830  81.98099  237.2 "Middle Africa"  
"AGO" 2014 486 "Bananas"                       3483432 1077.2948  308.8 "Middle Africa"  
"AGO" 2014 574 "Pineapples"                     599156   420.518  700.9 "Middle Africa"  
"ALB" 1993  27 "Rice, paddy"                       585   .425154  726.7 "Southern Europe"
"ALB" 1993  56 "Maize"                          175751   42.7409  243.2 "Southern Europe"
"ALB" 1993 116 "Potatoes"                       101527 32.539894  320.5 "Southern Europe"
"ALB" 1993 176 "Beans, dry"                      23509  10.50899    447 "Southern Europe"
"ALB" 1993 388 "Tomatoes"                       106038   96.8802  913.7 "Southern Europe"
"ALB" 1993 463 "Vegetables, fresh nes"           51400 22.471045  437.2 "Southern Europe"
"ALB" 1993 490 "Oranges"                         13300  6.767994  508.9 "Southern Europe"
"ALB" 1993 515 "Apples"                          10000  4.610771  461.1 "Southern Europe"
"ALB" 1993 536 "Plums and sloes"                  5600  1.527177  272.7 "Southern Europe"
"ALB" 1994  27 "Rice, paddy"                         0         0  570.7 "Southern Europe"
"ALB" 1994  56 "Maize"                          193261     40.44  209.3 "Southern Europe"
"ALB" 1994  71 "Rye"                              3765   .811703  215.6 "Southern Europe"
"ALB" 1994 116 "Potatoes"                        88918  30.07055  338.2 "Southern Europe"
"ALB" 1994 463 "Vegetables, fresh nes"           23100  9.862684    427 "Southern Europe"
"ALB" 1994 536 "Plums and sloes"                  7862  2.130532  275.8 "Southern Europe"
"ALB" 1995  15 "Wheat"                          405342  65.59109  161.8 "Southern Europe"
"ALB" 1995  27 "Rice, paddy"                         0         0    616 "Southern Europe"
"ALB" 1995  56 "Maize"                          215566  39.53313  183.4 "Southern Europe"
"ALB" 1995  75 "Oats"                            12989  2.802449  215.8 "Southern Europe"
"ALB" 1995 116 "Potatoes"                       133910 30.336416  226.5 "Southern Europe"
"ALB" 1995 176 "Beans, dry"                      20274 17.715624  873.8 "Southern Europe"
"ALB" 1995 260 "Olives"                          38763  9.617832  248.1 "Southern Europe"
"ALB" 1995 388 "Tomatoes"                       150000    48.545  323.6 "Southern Europe"
"ALB" 1995 490 "Oranges"                          3782  1.631975  431.5 "Southern Europe"
"ALB" 1995 515 "Apples"                          10000  3.236333  323.6 "Southern Europe"
"ALB" 1995 521 "Pears"                            3000  1.294533  431.5 "Southern Europe"
"ALB" 1995 531 "Cherries"                         3000  1.682893    561 "Southern Europe"
"ALB" 1995 536 "Plums and sloes"                 10000  3.236333  323.6 "Southern Europe"
"ALB" 1995 560 "Grapes"                          55493 15.923987    287 "Southern Europe"
end

The previous example does not illustrate that there are multiply countries per countrygroup, since my dataset is large. So in the following example, I show this (by considering only the year 2010):

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input str3 iso3code int(year itemcode) str44 item double production float(production_value prodprice) str39 countrygroup
"AUS" 2010  15 "Wheat"                                        21834010  4366.163    200 "Australia and New Zealand"
"AUS" 2010  27 "Rice, paddy"                                    196684  82.45086  419.2 "Australia and New Zealand"
"AUS" 2010  44 "Barley"                                        7864551 1240.8302  157.8 "Australia and New Zealand"
"AUS" 2010  75 "Oats"                                          1161606 170.48602  146.8 "Australia and New Zealand"
"AUS" 2010  83 "Sorghum"                                       1507635   271.058  179.8 "Australia and New Zealand"
"AUS" 2010 116 "Potatoes"                                      1278118  562.7586  440.3 "Australia and New Zealand"
"AUS" 2010 156 "Sugar cane"                                   31234824 1260.6708   40.4 "Australia and New Zealand"
"AUS" 2010 191 "Chick peas"                                     487046 193.00284  396.3 "Australia and New Zealand"
"AUS" 2010 210 "Lupins"                                         822963 187.97046  228.4 "Australia and New Zealand"
"AUS" 2010 234 "Nuts, nes"                                       37680  72.58388 1926.3 "Australia and New Zealand"
"AUS" 2010 270 "Rapeseed"                                      1907272  769.7953  403.6 "Australia and New Zealand"
"AUS" 2010 328 "Seed cotton"                                    939000 1843.2716   1963 "Australia and New Zealand"
"AUS" 2010 329 "Cottonseed"                                     550000  194.5353  353.7 "Australia and New Zealand"
"AUS" 2010 388 "Tomatoes"                                       471883  317.7169  673.3 "Australia and New Zealand"
"AUS" 2010 403 "Onions, dry"                                    259947 165.00642  634.8 "Australia and New Zealand"
"AUS" 2010 426 "Carrots and turnips"                            267442  161.1777  602.7 "Australia and New Zealand"
"AUS" 2010 449 "Mushrooms and truffles"                          41295 216.29353 5237.8 "Australia and New Zealand"
"AUS" 2010 486 "Bananas"                                        302173  447.6495 1481.4 "Australia and New Zealand"
"AUS" 2010 490 "Oranges"                                        391343 280.00266  715.5 "Australia and New Zealand"
"AUS" 2010 495 "Tangerines, mandarins, clementines, satsumas"    91002 113.52717 1247.5 "Australia and New Zealand"
"AUS" 2010 515 "Apples"                                         264401   368.652 1394.3 "Australia and New Zealand"
"AUS" 2010 521 "Pears"                                           95111 68.051125  715.5 "Australia and New Zealand"
"AUS" 2010 534 "Peaches and nectarines"                          77683 103.32465 1330.1 "Australia and New Zealand"
"AUS" 2010 544 "Strawberries"                                    29334 194.81384 6641.2 "Australia and New Zealand"
"AUS" 2010 560 "Grapes"                                        1684345 1018.1844  604.5 "Australia and New Zealand"
"AUS" 2010 571 "Mangoes, mangosteens, guavas"                    44342  103.7207 2339.1 "Australia and New Zealand"
"AUS" 2010 767 "Cotton lint"                                    352049   2530.98 6543.4 "Australia and New Zealand"
"NZL" 2010  15 "Wheat"                                          444890 130.35107    293 "Australia and New Zealand"
"NZL" 2010  44 "Barley"                                         308298  79.08302  256.5 "Australia and New Zealand"
"NZL" 2010  56 "Maize"                                          188812  43.53535  230.6 "Australia and New Zealand"
"NZL" 2010  75 "Oats"                                            47608  14.64773  307.7 "Australia and New Zealand"
"NZL" 2010 187 "Peas, dry"                                       37094 18.896685  509.4 "Australia and New Zealand"
"NZL" 2010 515 "Apples"                                         444154 148.87888  335.1 "Australia and New Zealand"
"NZL" 2010 592 "Kiwi fruit"                                     434120  401.9532  925.9 "Australia and New Zealand"
"BRB" 2010 122 "Sweet potatoes"                                   1176  2.774117 2358.9 "Caribbean"                
"BRB" 2010 125 "Cassava"                                           400   .599657 1499.1 "Caribbean"                
"BRB" 2010 137 "Yams"                                              807  1.832502 2270.8 "Caribbean"                
"BRB" 2010 358 "Cabbages and other brassicas"                       60   .144182   2403 "Caribbean"                
"BRB" 2010 388 "Tomatoes"                                          718  2.176511 3031.4 "Caribbean"                
"BRB" 2010 394 "Pumpkins, squash and gourds"                       180   .214289 1190.5 "Caribbean"                
"BRB" 2010 397 "Cucumbers and gherkins"                           1148  1.784287 1554.3 "Caribbean"                
"BRB" 2010 401 "Chillies and peppers, green"                       394   1.56786 3979.3 "Caribbean"                
"BRB" 2010 423 "String beans"                                      222  1.120785 5048.6 "Caribbean"                
"BRB" 2010 426 "Carrots and turnips"                               264   .905041 3428.2 "Caribbean"                
"BRB" 2010 430 "Okra"                                              303    .58784 1940.1 "Caribbean"                
"BRB" 2010 568 "Melons, other (inc.cantaloupes)"                   241   .353323 1466.1 "Caribbean"                
"DOM" 2010  27 "Rice, paddy"                                    850228  391.0197  459.9 "Caribbean"                
"DOM" 2010  56 "Maize"                                           35078 13.208626  376.5 "Caribbean"                
"DOM" 2010  83 "Sorghum"                                          1150    .30585  265.9 "Caribbean"                
"DOM" 2010 116 "Potatoes"                                        52381 24.655537  470.7 "Caribbean"                
"DOM" 2010 122 "Sweet potatoes"                                  53345  14.96302  280.5 "Caribbean"                
"DOM" 2010 125 "Cassava"                                        204920  53.27082    260 "Caribbean"                
"DOM" 2010 135 "Yautia (cocoyam)"                                29621  24.69541  833.7 "Caribbean"                
"DOM" 2010 137 "Yams"                                            26958  20.23583  750.6 "Caribbean"                
"DOM" 2010 156 "Sugar cane"                                    4577122   110.196   24.1 "Caribbean"                
"DOM" 2010 176 "Beans, dry"                                      33021 36.168846 1095.3 "Caribbean"                
"DOM" 2010 197 "Pigeon peas"                                     23536 14.977043  636.3 "Caribbean"                
"DOM" 2010 242 "Groundnuts, with shell"                           3841  2.678128  697.3 "Caribbean"                
"DOM" 2010 249 "Coconuts"                                       128370 33.084774  257.7 "Caribbean"                
"DOM" 2010 358 "Cabbages and other brassicas"                    42689  18.71303  438.4 "Caribbean"                
"DOM" 2010 372 "Lettuce and chicory"                              3327  3.129794  940.7 "Caribbean"                
"DOM" 2010 388 "Tomatoes"                                       240254   153.831  640.3 "Caribbean"                
"DOM" 2010 394 "Pumpkins, squash and gourds"                     38246 14.035492    367 "Caribbean"                
"DOM" 2010 397 "Cucumbers and gherkins"                           6945   1.58207  227.8 "Caribbean"                
"DOM" 2010 399 "Eggplants (aubergines)"                          22244  8.031401  361.1 "Caribbean"                
"DOM" 2010 401 "Chillies and peppers, green"                     37026  29.07891  785.4 "Caribbean"                
"DOM" 2010 403 "Onions, dry"                                     48534  47.18024  972.1 "Caribbean"                
"DOM" 2010 406 "Garlic"                                           2001  6.206559 3102.4 "Caribbean"                
"DOM" 2010 426 "Carrots and turnips"                             26533  8.764905  330.3 "Caribbean"                
"DOM" 2010 486 "Bananas"                                        892753 107.41273  120.3 "Caribbean"                
"DOM" 2010 489 "Plantains and others"                           460254 169.28397  367.8 "Caribbean"                
"DOM" 2010 490 "Oranges"                                        138034 23.035366  166.9 "Caribbean"                
"DOM" 2010 497 "Lemons and limes"                                11909   .740328   62.2 "Caribbean"                
"DOM" 2010 507 "Grapefruit (inc. pomelos)"                       17109  21.78953 1273.6 "Caribbean"                
"DOM" 2010 568 "Melons, other (inc.cantaloupes)"                 20447  6.503925  318.1 "Caribbean"                
"DOM" 2010 571 "Mangoes, mangosteens, guavas"                     7867  3.250513  413.2 "Caribbean"                
"DOM" 2010 572 "Avocados"                                       285590 110.59303  387.2 "Caribbean"                
"DOM" 2010 574 "Pineapples"                                     165724    38.901  234.7 "Caribbean"                
"DOM" 2010 600 "Papayas"                                        498071   99.0816  198.9 "Caribbean"                
"DOM" 2010 656 "Coffee, green"                                   21876   56.0862 2563.8 "Caribbean"                
"DOM" 2010 661 "Cocoa, beans"                                    58334 134.20418 2300.6 "Caribbean"                
"DOM" 2010 826 "Tobacco, unmanufactured"                          8066  23.60285 2926.2 "Caribbean"                
"GRD" 2010  56 "Maize"                                             343   .278487  816.5 "Caribbean"                
"GRD" 2010 122 "Sweet potatoes"                                    125   .179061 1428.9 "Caribbean"                
"GRD" 2010 125 "Cassava"                                           217   .132696  612.4 "Caribbean"                
"GRD" 2010 137 "Yams"                                              529   .647979 1224.8 "Caribbean"                
"GRD" 2010 149 "Roots and tubers, nes"                            2228  2.889316 1298.3 "Caribbean"                
"GRD" 2010 176 "Beans, dry"                                        117   .209491 1786.2 "Caribbean"                
"GRD" 2010 197 "Pigeon peas"                                       740  1.386155 1837.2 "Caribbean"                
"GRD" 2010 249 "Coconuts"                                         6474  7.929283 1224.8 "Caribbean"                
"GRD" 2010 358 "Cabbages and other brassicas"                      189   .359749 1905.2 "Caribbean"                
"GRD" 2010 372 "Lettuce and chicory"                                99   .106864 1088.7 "Caribbean"                
"GRD" 2010 388 "Tomatoes"                                          261   .549447 2109.4 "Caribbean"                
"GRD" 2010 393 "Cauliflowers and broccoli"                          23   .074746 3266.1 "Caribbean"                
"GRD" 2010 394 "Pumpkins, squash and gourds"                       326   .346289 1061.5 "Caribbean"                
"GRD" 2010 397 "Cucumbers and gherkins"                            139   .169698 1224.8 "Caribbean"                
"GRD" 2010 426 "Carrots and turnips"                                77   .141305 1837.2 "Caribbean"                
"GRD" 2010 463 "Vegetables, fresh nes"                            2185  3.887665 1777.3 "Caribbean"                
"GRD" 2010 486 "Bananas"                                          2703  1.260492  466.6 "Caribbean"                
"GRD" 2010 489 "Plantains and others"                              235   .240194 1020.7 "Caribbean"                
end


What I would like to do is estimate regional averages for the price of each item. I figured it would look something like -bys countrygroup year itemcode: mean(prodprice), but the problem is that I would like the regional averages to be weighted by a country's production of the item, and I'm not sure how I could add this to the code. I am aware of Stata modules that are written that could do this, but I always try to improve my understanding of Stata before I resort to Stata modules.

If someone has any suggestions how I could achieve this, it would be greatly appreciated. Ofcourse, if using a Stata module is in the end the best thing to do here, I would happily do that.

Best,

Satya