So I want to subset my data frame to select rows with a daily maximum value.
Site Year Day Time Cover Size TempChange
ST1 2011 97 0.0 Closed small 0.97
ST1 2011 97 0.5 Closed small 1.02
ST1 2011 97 1.0 Closed small 1.10
Section of data frame is above. I would like to select only the rows which have the maximum value of the variable TempChange for each variable Day. I want to do this because I am interested in specific variables (not shown) for these particular times.
AMENDED EXAMPLE AND REQUIRED OUTPUT
Site Day Temp Row
a 10 0.2 1
a 10 0.3 2
a 11 0.5 3
a 11 0.4 4
b 10 0.1 5
b 10 0.8 6
b 11 0.7 7
b 11 0.6 8
c 10 0.2 9
c 10 0.3 10
c 11 0.5 11
c 11 0.8 12
REQUIRED OUTPUT
Site Day Temp Row
a 10 0.3 2
a 11 0.5 3
b 10 0.8 6
b 11 0.7 7
c 10 0.3 10
c 11 0.8 12
Hope that makes it clearer.