[R] Unique subsetting question

[AndrewPage]

Hi all,

I'm looking at a large data set, and I'm interested in removing rows where
only one variable is duplicated.  Here's an example:

> presidents
     Qtr1 Qtr2 Qtr3 Qtr4
1945   NA   87   82   75
1946   63   50   43   32
1947   35   60   54   55
1948   36   39   NA   NA
1949   69   57   57   51
1950   45   37   46   39
1951   36   24   32   23
1952   25   32   NA   32
1953   59   74   75   60
1954   71   61   71   57
1955   71   68   79   73
1956   76   71   67   75
1957   79   62   63   57
1958   60   49   48   52
1959   57   62   61   66
1960   71   62   61   57
1961   72   83   71   78
1962   79   71   62   74
1963   76   64   62   57
1964   80   73   69   69
1965   71   64   69   62
1966   63   46   56   44
1967   44   52   38   46
1968   36   49   35   44
1969   59   65   65   56
1970   66   53   61   52
1971   51   48   54   49
1972   49   61   NA   NA
1973   68   44   40   27
1974   28   25   24   24

See how in 1954 and 1955, the Qtr1 approval rating is the same?  Let's say I
wanted to return the presidents data frame, but only have unique values for
Qtr1.  I doesn't matter which years are displayed for duplicated values-- it
just matters that each value is not displayed more than once.  Any way I can
do this but still have it be a data frame that shows Qtr2, 3, and 4 values?

Thanks in advance,
Andrew
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