[R] Arrange data

[Md. Moyazzem Hossain]

Hi,

I have a dataset having monthly observations (from January to December)
over a period of time like (2000 to 2018). Now, I am trying to take an
average the value from January to July of each year.

The data looks like
Year    Month  Value
2000    1         25
2000    2         28
2000    3         22
....    ......      .....
2000    12       26
2001     1       27
.......         ........
2018    11       30
20118   12      29

Can someone help me in this regard?

Many thanks in advance.

*Regards,*
*Md*

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