如何应用操作data.table的函数并将2个或多个值用作参数R

Question

I have the following data.table

k
   v1 v2 v3   v4
1:  1 US  a   up
2:  2 CA  a   up
3:  3 US  b down
4:  4 CA  a down
5:  5 US  b   up
6:  6 CA  b down

And I want to recreate the following operation using a function

k[v3 %in% unique(k$v3) & v4=="up",list("sum" = sum(v1)),by=v2]
   v2 sum
1: US   6
2: CA   2

So far I got this

myfun <- function(x,y,z) {
w <- x[v3 %in% y & v4 %in% z,list("sum" = sum(v1)),by=v2]
  print(w)
}
myfun(k,"a","up")
   v2 sum
1: US   1
2: CA   2

How can I enhance this function to be able to use more than one parameter in each expression, y,z. I have tried with the following function, setting an option called "All" that is a vector of all unique values of each column but it returns a data.table with zero rows

myfun <- function(x,y,z) {

  ifelse(y == "All" ,y==unique(x$v3),y==y)
  ifelse(z == "All" ,z==unique(x$v2),z==z)

  w <- x[v3 %in% y & v4 %in% z,list("sum" = sum(v1)),by=v2]
  print(w)
}

Answer 1

This should get you started:

myfun <- function(x,y,z) {
  if (length(y) == 1 && y == "All") {
    cond1 = TRUE
  } else {
    cond1 = quote(v3 %in% y)
  }

  if (length(z) == 1 && z == "All") {
    cond2 = TRUE
  } else {
    cond2 = quote(v4 %in% z)
  }

  x[eval(cond1) & eval(cond2), list("sum" = sum(v1)), by=v2]
}

myfun(k, "a", "up")
#   v2 sum
#1: US   1
#2: CA   2

myfun(k, "All", "up")
#   v2 sum
#1: US   6
#2: CA   2