从 data.table 中的每个组中减去一个向量，并按日期匹配

Question

Suppose I have a data.table like this:

print(priceDT)

          Date  Return Stock
 1: 2011-01-03  0.0800   AFR
 2: 2011-01-04  0.0300   AFR
 3: 2011-01-05 -0.0125   AFR
 4: 2011-01-06  0.0100   AFR
 5: 2011-01-07  0.0020   AFR
 6: 2011-01-10  0.0073   BMF
 7: 2011-01-11 -0.0150   BMF
 8: 2011-01-12  0.0130   BMF
 9: 2011-01-13 -0.0080   BMF
10: 2011-01-14  0.0410   BMF
11: 2011-01-17 -0.0065   BMF
12: 2011-01-18  0.0180   BMF
13: 2011-01-19  0.0017   BMF
14: 2011-01-20  0.0262   BMF
15: 2011-01-21 -0.0190   BMF

I want to subtract a vector of market returns from the returns column in the priceDT data.table. The market returns is in another data.table and contains dates from the first 3 trading weeks in 2011. However, the two stocks in the priceDT do not have data for all of the trading weeks. The first stock, AFR, only has one week of data. The second stock has two weeks of data. The market returns have all three weeks of data.

The market returns looks like this:

print(market)

 market
          Date   Return
 1: 2011-01-03  0.01112
 2: 2011-01-04  0.02800
 3: 2011-01-05  0.00580
 4: 2011-01-06  0.00400
 5: 2011-01-07  0.00910
 6: 2011-01-10  0.01300
 7: 2011-01-11 -0.00800
 8: 2011-01-12 -0.01000
 9: 2011-01-13  0.02400
10: 2011-01-14  0.01390
11: 2011-01-17  0.01040
12: 2011-01-18  0.00718
13: 2011-01-19  0.01220
14: 2011-01-20 -0.00620
15: 2011-01-21  0.00944

How do I subtract the market returns of the first week of January from the returns of the first stock, AFR and substract the market returns of the next two weeks of January from the returns of the second stock, BMF. Is there a way to match by dates in both data before subtracting?

The result should be:

print(result)

          Date  Return Adjusted Return Stock
 1: 2011-01-03  0.0800         0.06888   AFR
 2: 2011-01-04  0.0300         0.00200   AFR
 3: 2011-01-05 -0.0125        -0.01830   AFR
 4: 2011-01-06  0.0100         0.00600   AFR
 5: 2011-01-07  0.0020        -0.00710   AFR
 6: 2011-01-10  0.0073        -0.00570   BMF
 7: 2011-01-11 -0.0150        -0.00700   BMF
 8: 2011-01-12  0.0130         0.02300   BMF
 9: 2011-01-13 -0.0080        -0.03200   BMF
10: 2011-01-14  0.0410         0.02710   BMF
11: 2011-01-17 -0.0065        -0.01690   BMF
12: 2011-01-18  0.0180         0.01082   BMF
13: 2011-01-19  0.0017        -0.01050   BMF
14: 2011-01-20  0.0262         0.03240   BMF
15: 2011-01-21 -0.0190        -0.02844   BMF

Data:

priceDT <- fread(text = "Date,Return,Stock
                 2011-01-03,0.08,AFR
                 2011-01-04,0.03,AFR
                 2011-01-05,-0.0125,AFR
                 2011-01-06,0.01,AFR
                 2011-01-07,0.002,AFR
                 2011-01-10,0.0073,BMF
                 2011-01-11,-0.015,BMF
                 2011-01-12,0.013,BMF
                 2011-01-13,-0.008,BMF
                 2011-01-14,0.041,BMF
                 2011-01-17,-0.0065,BMF
                 2011-01-18,0.018,BMF
                 2011-01-19,0.0017,BMF
                 2011-01-20,0.0262,BMF
                 2011-01-21,-0.019,BMF
                                 ")

market <- fread(text = "Date,Return
                 2011-01-03,0.01112
                 2011-01-04,0.028
                 2011-01-05,0.0058
                 2011-01-06,0.004
                 2011-01-07,0.0091
                 2011-01-10,0.013
                 2011-01-11,-0.008
                 2011-01-12,-0.01
                 2011-01-13,0.024
                 2011-01-14,0.0139
                 2011-01-17,0.0104
                 2011-01-18,0.00718
                 2011-01-19,0.0122
                 2011-01-20,-0.0062
                 2011-01-21,0.00944
                ")

result <- fread(text = "Date,Return,Adjusted Return,Stock
                 2011-01-03,0.08,0.06888,AFR
                 2011-01-04,0.03,0.00200,AFR
                 2011-01-05,-0.0125,-0.01830,AFR
                 2011-01-06,0.01,0.00600,AFR
                 2011-01-07,0.002,-0.00710,AFR
                 2011-01-10,0.0073,-0.0057,BMF
                 2011-01-11,-0.015,-0.0070,BMF
                 2011-01-12,0.013,0.0230,BMF
                 2011-01-13,-0.008,-0.0320,BMF
                 2011-01-14,0.041,0.0271,BMF
                 2011-01-17,-0.0065,-0.0169,BMF
                 2011-01-18,0.018,0.01082,BMF
                 2011-01-19,0.0017,-0.0105,BMF
                 2011-01-20,0.0262,0.03240,BMF
                 2011-01-21,-0.019,-0.02844,BMF
                ")

Answer 1

I might have misunderstood your requirements but this matches the expected output

priceDT[, adj_return := market[.SD, on = "Date", i.Return - x.Return]]