[R] finding the annual maximun within several years

["Dörte Salecker"]

dear r-helpers

i've got a table that in extracts looks like this:

           V1       V2      V3    V4      V5
1  01/01/1975 00:00:00 125.837 3.691 296.618
2  01/01/1975 01:00:00 124.799 3.679 281.307
3  01/01/1975 02:00:00 111.607 3.536 281.307
4  02/24/1976 11:00:00  21.602 2.555  93.893
5  02/24/1976 12:00:00  27.804 2.623  93.893
6  02/24/1976 13:00:00  26.105 2.604 114.716
7  10/18/1977 00:00:00  18.850 2.525 330.203
8  10/18/1977 01:00:00  21.561 2.555 320.465
9  10/18/1977 02:00:00  21.941 2.559 314.505
10 11/05/1978 01:00:00  24.981 2.592 310.464
11 11/05/1978 02:00:00  19.066 2.528 310.464
12 11/05/1978 03:00:00  26.198 2.605 305.749
13 06/29/1979 19:00:00  78.829 3.179 306.199
14 06/29/1979 20:00:00  92.221 3.325 306.199
15 06/29/1979 21:00:00  72.364 3.108 303.049

i need to find the annual maximun for each year in V3, V4 and V5 So that the result would be a table like this:

           V1	   V4
1  01/01/1975 	3.691 
2  02/24/1976   2.623
3  10/18/1977   2.559
.
.
.and so on.

i hope you can help me with this,

thank you in advance,
doerte

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