[External Email] Group by and add a constant value based on a condition dply

Hi everyone,

I have the following dataframe:



      structure(list(Department = c("A", "A", "A", "A", "A", "A", "A",
     "A", "B", "B", "B", "B", "B", "B", "B", "B"), Class = c(1L, 1L,
    1L, 1L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L), Value = c(0L,
    100L, 800L, 800L, 0L, 300L, 1200L, 0L, 0L, 0L, 400L, 400L, 200L,
    800L, 1200L, 0L), Date = c("1.01.2020", "2.01.2020", "3.01.2020",
    "4.01.2020", "1.01.2020", "2.01.2020", "3.01.2020", "4.01.2020",
    "1.01.2020", "2.01.2020", "3.01.2020", "4.01.2020", "1.01.2020",
    "2.01.2020", "3.01.2020", "4.01.2020")), class = "data.frame",
row.names = c(NA,
     -16L))

 using dplyr I need to group by "Depatment" and "Class" and then for all
the dates that are "4.01.2020"  and have the "Value" greater than zero  add
5 to the "Value", meaning the desired dataframe will be (NewValue column) :



   structure(list(Department = c("A", "A", "A", "A", "A", "A", "A",
 "A", "B", "B", "B", "B", "B", "B", "B", "B"), Class = c(1L, 1L,
 1L, 1L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L), Value = c(0L,
 100L, 800L, 800L, 0L, 300L, 1200L, 0L, 0L, 0L, 400L, 400L, 200L,
 800L, 1200L, 0L), Date = c("1.01.2020", "2.01.2020", "3.01.2020",
 "4.01.2020", "1.01.2020", "2.01.2020", "3.01.2020", "4.01.2020",
 "1.01.2020", "2.01.2020", "3.01.2020", "4.01.2020", "1.01.2020",
 "2.01.2020", "3.01.2020", "4.01.2020"), NewValue = c(0L, 100L,
 800L, 805L, 0L, 300L, 1200L, 0L, 0L, 0L, 400L, 405L, 200L, 800L,
 1200L, 0L)), class = "data.frame", row.names = c(NA, -16L))


Thanks a lot for any help!
Elahe