重复的else if语句的快捷方式

Question

I have to write repetitive else if conditions like:

  if (d_hand[1]==1){
    state=score(p_hand)-1
  } else if (d_hand[1]==2){
    state=19+score(p_hand)
  } else if (d_hand[1]==3){
    state=39+score(p_hand)
  } else if (d_hand[1]==4){
    state=59+score(p_hand)
  } else if (d_hand[1]==5){
    state=79+score(p_hand)
  } else if (d_hand[1]==6){
    state=99+score(p_hand)
  }

Do you know if it could be written more efficiently/shortly? I thought about doing a loop of if but it would be less efficient since every statement would have to be examined.

Answer 1

ifelse没有ifelse ：

state <- score(p_hand) + 20 * d_hand[1] - 21

Answer 2

Maybe a lookup table.

add <- c(-1, 19, 39, 59, 79, 99)
state <- add[which(1:6 == d_hand[1])] + score(p_hand)

Answer 3

You can either use switch from base, or dplyr case_when :

library(dplyr)
state <- case_when(d_hand[1]==1 ~ {score(p_hand)-1}, 
          d_hand[1]==2 ~ 19+score(p_hand), 
          d_hand[1]==3 ~ 39+score(p_hand), 
          d_hand[1]==4 ~ 59+score(p_hand),
          d_hand[1]==5 ~ 79+score(p_hand), 
          d_hand[1]==6 ~ 99+score(p_hand)
)

Answer 4

This logic is very close to @Martin.

state <- score(p_hand) + 20*(d_hand[1]-1) - 1

EDIT I had thought to gain some performance benefit but I had missed one point. I'll share details of microbenchmark performance later. But performance of @Martin is better than mine (which obvious).