[R] data format issue

[Sherri Heck]

Dear all-

I have a dataset (see a sample below - but the whole dataset is June 
2005 - June 2008).  The "LST" format is "YYMMDDHHmm" and I would like to 
get the hourly average of the "mph" for the summer months (spanning all 
years). I have been trying to use "aggregate" but am not having much 
success at all!  any thoughts would be greatly appreciated.

thanks-

sherri

    LST   inch     mph    Deg   DegF  DegF    %    volts   Deg    mph   
w/m2
0506010000   0.00   13.6  218.1   36.8   -999   65.1   -999   -999   
18.2    0.2
0506010005   0.00   12.9  214.3   36.8   -999   65.5   -999   -999   
16.9    0.2
0506010010   0.00   14.4  215.7   36.9   -999   65.4   -999   -999   
20.4    0.2
0506010015   0.00   13.8  215.8   36.8   -999   65.7   -999   -999   
19.7    0.3
0506010020   0.00   11.9  213.4   36.8   -999   65.6   -999   -999   
14.6    0.2
0506010025   0.00   12.7  212.4   36.8   -999   65.4   -999   -999   
16.9    0.2
0506010030   0.00   14.1  215.8   36.8   -999   65.9   -999   -999   
19.1    0.2
0506010035   0.00   14.8  217.2   36.7   -999   66.2   -999   -999   
20.4    0.2
0506010040   0.00   16.2  222.0   36.8   -999   66.6   -999   -999   
20.2    0.2
0506010045   0.00   13.6  219.5   36.7   -999   66.6   -999   -999   
18.4    0.2
0506010050   0.00   14.8  217.6   36.7   -999   66.2   -999   -999   
20.0    0.2
0506010055   0.00   13.1  214.8   36.7   -999   65.9   -999   -999   
20.2    0.2
0506010100   0.00   12.2  214.3   36.7   -999   65.2   -999   -999   
15.6    0.2
0506010105   0.00   14.2  207.8   36.7   -999   65.0   -999   -999   
19.9    0.2
0506010110   0.00   15.4  207.0   36.7   -999   64.4   -999   -999   
20.2    0.2
0506010115   0.00   17.2  205.9   36.7   -999   64.5   -999   -999   
22.1    0.2
0506010120   0.00   16.8  208.9   36.8   -999   65.0   -999   -999   
21.9    0.2
0506010125   0.00   18.4  214.0   36.9   -999   65.1   -999   -999   
26.4    0.2
0506010130   0.00   17.3  214.7   37.0   -999   65.5   -999   -999   
24.0    0.2
0506010135   0.00   18.4  214.3   37.1   -999   65.2   -999   -999   
24.9    0.2
0506010140   0.00   19.6  216.6   37.3   -999   65.3   -999   -999   
26.7    0.2
0506010145   0.00   19.7  220.5   37.5   -999   65.1   -999   -999   
27.5    0.2
0506010150   0.00   19.6  215.5   37.6   -999   64.6   -999   -999   
26.4    0.2
0506010155   0.00   21.8  220.1   37.8   -999   64.1   -999   -999   
31.2    0.2
0506010200   0.00   23.4  222.9   37.9   -999   63.8   -999   -999   
31.8    0.2
0506010205   0.00   24.0  221.7   37.9   -999   63.7   -999   -999   
30.3    0.2
0506010210   0.00   24.2  223.4   38.0   -999   63.5   -999   -999   
28.2    0.2
0506010215   0.00   23.8  224.9   38.0   -999   63.4   -999   -999   
30.3    0.2
0506010220   0.00   23.9  225.1   38.1   -999   63.5   -999   -999   
29.5    0.2
0506010225   0.00   23.9  227.4   38.1   -999   63.5   -999   -999   
30.3    0.2
0506010230   0.00   23.9  226.0   38.0   -999   63.6   -999   -999   
27.5    0.2
0506010235   0.00   21.5  221.4   38.0   -999   63.7   -999   -999   
28.4    0.2
0506010240   0.00   22.3  222.6   37.9   -999   63.8   -999   -999   
27.9    0.2
0506010245   0.00   21.5  223.9   37.9   -999   64.0   -999   -999   
28.4    0.2
0506010250   0.00   22.2  226.7   37.8   -999   64.2   -999   -999   
27.7    0.2
0506010255   0.00   21.9  223.5   37.8   -999   64.3   -999   -999   
26.9    0.2
0506010300   0.00   22.0  223.2   37.7   -999   64.3   -999   -999   
28.0    0.2