[R] About change columns and specific rows in R

[lily li]

Hi R users,

I have a question about manipulating the dataframe. I want to create a new
dataframe, and to multiply rows with different seasons for different
constants.

DF
year   month   day   product1   product2   product3
1981     1          1         18              56            20
1981     1          2         19              45            22
1981     1          3         16              48            28
1981     1          4         19              50            21
1981     2          1         17              49            25
1981     2          2         20              47            23
1981     2          3         21              52            27

For example, how to multiply product1 in month1 by 3.1, and to multiply
product3 in month2 by 2.0? I wrote the code like this but does not work.
Thanks for your help.

DF['month'==1, ]$product1_1 = DF['month'==1, ]$product1 * 3.1;
DF['month'==2, ]$product3_1 = DF['month'==1, ]$product3 * 2.0;

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