[R] Merge of the rows by finding the sum of the rows

[Hafizuddin Arshad]

Dear R users,

Can someone help me on this?  I would like to find the sum of the Rain if
the Month appears more than once. For example in row 3 and 4, October
appear more than once, so I want to find the sum of the two rows and
replace it so that the Month just appear once. It some sort of merge but by
finding the sum for the third column. This is my data:

structure(list(Year = c(1971L, 1971L, 1971L, 1971L, 1971L, 1971L,
1971L, 1971L, 1971L, 1972L, 1972L, 1972L, 1972L, 1972L, 1972L,
1973L, 1973L, 1973L, 1973L, 1973L, 1973L, 1973L, 1973L, 1973L,
1973L, 1974L, 1974L, 1974L, 1974L, 1974L, 1974L, 1974L, 1974L,
1974L, 1975L, 1975L, 1975L, 1975L, 1975L, 1975L, 1975L, 1976L,
1976L, 1976L, 1976L, 1976L, 1976L, 1976L, 1976L, 1976L), Month = c(3L,
6L, 10L, 10L, 11L, 11L, 11L, 11L, 12L, 2L, 9L, 12L, 12L, 12L,
12L, 3L, 9L, 10L, 11L, 11L, 11L, 11L, 12L, 12L, 12L, 8L, 9L,
11L, 11L, 11L, 11L, 11L, 12L, 12L, 1L, 2L, 4L, 10L, 11L, 12L,
12L, 10L, 11L, 11L, 11L, 11L, 11L, 11L, 11L, 11L), Rain = c(196,
88.8, 96, 70.6, 104.9, 80, 102.8, 161.5, 123.4, 70.8, 99, 77.7,
130.8, 134.1, 86.3, 213.3, 169.9, 89.4, 78.7, 81.5, 100.3, 107.1,
93.2, 83.8, 253.2, 75.4, 134.5, 84.5, 82.5, 82.5, 119.5, 119.5,
134.5, 83.5, 372.5, 79.5, 112, 80.5, 129.5, 120.5, 126, 73, 93.5,
86.5, 140.5, 76, 180.5, 75, 130.5, 130.5)), .Names = c("Year",
"Month", "Rain"), row.names = c(NA, 50L), class = "data.frame")

Thank you so much for the help.


Arshad

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