r - How can I do a left join in data.table, Y[X], for two tables with different names, and keep the column names for X? -


when conducting left join using y[x] in data.table tables different names, retain column names table x, here denoted myx. 

myx <- data.table(value = 1:10, key1 = letters[1:10], key2 = toupper(letters[1:10]) )  myy <- data.table(value2 = 101:120, diffkey1 = letters[1:20], diffkey2 = toupper(letters[1:20]) )   setkey(myx, 'key1', 'key2') setkey(myy, 'diffkey1', 'diffkey2')  (myx <- myy[myx])       value2 diffkey1 diffkey2 value 1:    101                   1 2:    102        b        b     2 3:    103        c        c     3 4:    104        d        d     4 5:    105        e        e     5 6:    106        f        f     6 7:    107        g        g     7 8:    108        h        h     8 9:    109                   9 10:    110       j        j    10  # step avoid setnames(myx,      old = c('diffkey1', 'diffkey2'),      new = c('key1', 'key2'))

at end have reset names , avoid step.

would consider changing name of key @ beginning?

    myx <- data.table(value = 1:10, key1 = letters[1:10], key2 = toupper(letters[1:10]) )      myy <- data.table(value2 = 101:120, key1 = letters[1:20], key2 = toupper(letters[1:20]) )       setkey(myx, 'key1', 'key2')     setkey(myy, 'key1', 'key2')      (myx <- myy[myx])

or can reverse everything

    library(data.table)     myx <- data.table(value = 1:10, diffkey1 = letters[1:10], diffkey2 = toupper(letters[1:10]) )      myy <- data.table(value2 = 101:120, key1 = letters[1:20], key2 = toupper(letters[1:20]) )       setkey(myx, 'diffkey1', 'diffkey2')     setkey(myy, 'key1', 'key2')      (myx <- myy[myx])

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