[R] Using 'aggregate' when dependent on row value increments

Steve Murray
Thu, 30 Apr 2009 15:50:11 -0000

Dear all,

I have a data frame of three columns, which I have sorted by Latitude as
follows:

> test2[60:80,]
      Latitude Longitude  Sim_1986
61948    85.25    -29.25  2.175345
61957    85.25    -28.75  8.750486
61967    85.25    -28.25 33.569305
61977    85.25    -27.75 23.702572
61988    85.25    -27.25 26.488602
62000    85.25    -26.75 23.915724
62012    85.25    -26.25 25.055082
62027    85.25    -25.75 26.609823
62047    85.25    -25.25 28.813068
62066    84.25    -24.75 25.069952
52341    84.75    -82.25 34.940380
52434    84.75    -81.75 56.192116
52531    84.75    -81.25 41.409431
52616    83.75    -80.75 56.717590
52701    83.75    -80.25 68.887123
52781    83.75    -79.75 74.133286
52865    83.75    -79.25 41.309422
52951    82.25    -78.75 69.863419
53052    82.25    -78.25 21.480116
53164    82.25    -77.75 58.799141
55979    82.25    -68.75 70.028358


What I am hoping to do is to use the aggregate command to calculate the mean of
Sim_1986' per 1-degree increment of Latitude. So, using the above subset of
the data frame as an example, a mean would be produced based on the Sim_1986
values between where Latitude 85, 84, 83, 82. The maximum latitude in the
dataset as a whole is 83.75 and the minimum is -55.75.

Is it possible to also output corresponding latitude values for each
'grouped mean', so that I can easily associate each mean value with its
latitudinal band?


Many thanks for any help offered,

Steve


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