Dear all,
  Does R have function or method to finish the following task.
Say i have a dataset. The response variable is Y, and the indepedent
variables are X1, X2, X3, and YEAR. See an example.
Y              X1            X2            X3          X4            YEAR
13.4         2.8           3.5              2.5      1.8          1990
10.5        1.8            2.4              2          3           1991
            ....          .....
 In ecology, Y may be not only related with X1, X2, X3 in the same year as
Y, but also may be related with X1, X2, X3 and Y in the previous one , two
or more years as Y. But which year has the closest relationship is not know
and this may be one of the analysis aim.
Take Year=1995 as an example,
 Y_1995 may be related with
      X1_1995 , X2_1995 , X3_1995,
      X1_1994 , X2_1994 , X3_1994,  Y_1994,   (previous one year)
     X1_1993 , X2_1993 , X3_1993, Y_1993      (previous two years)
                ...         ...
(previous more years)
  Pay attention to the situation that Y itself may also affect its own value
of the next several years.
   Anybody knows whether R have functions or methods to
finish the above task.
  I hope i have explained it clearly. Any suggestions or help are greatly
appreciated.

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