不能 return 基于参数的数据框中的值

Question

如果这是一个非常直接或重复的问题，我深表歉意，但我似乎无法获得或找到正确的解决方案。

我只是想 return 一个基于输入的函数的速率。所以如果我的数据框是：

   January   0.02
  February   0.04
     March   0.06
     April   0.08
       May   0.10
      June   0.12
      July   0.14
    August   0.16
 September   0.18
   October   0.20
  November   0.22
  December   0.24

我正在尝试 return 基于输入的增长。所以调用 monthly_growth(August) 应该 return 0.16.

如果这是一个基本问题并且非常简单，我深表歉意，但我似乎无法解决 - 提前致谢。

Answer 1

简单示例程序：

mon <- c("January","February","March","April","May","June","July","August","September","October","November","December")
rate <- c(0.02,0.04,0.06,0.08,0.10,0.12,0.14,0.16,0.18,0.20,0.22,0.24)

#create the dataframe to use for lookups
df <- data.frame(mon,rate)

#custom function - returns the rate for the month passed in.  No error checking
monthly_growth <- function(theMonth){
  return(df[df$mon==theMonth,"rate"])
}

#example usage
monthly_growth("August")
monthly_growth("October")

Answer 2

另一种选择，如果您只使用月份作为切换到汇率的输入，您可以使用 switch 函数：

getRate <- function(month) {
  switch(month,
         January = 0.02,
         February = 0.04,
         March = 0.06,
         April = 0.08,
         May = 0.1,
         June = 0.12,
         July = 0.14,
         August = 0.16,
         September = 0.18,
         October = 0.2,
         November = 0.22,
         December = 0.24,
         "Invalid month.")
}

getRate("August")
# [1] 0.16
getRate("hello")
# [1] "Invalid month."

仅供参考，稍微费点功夫，您就可以使该函数适用于不同 "month" 值的任何大写和月份缩写的任何大写，带或不带引号：

getRate2 <- function(month) {
  month <- tolower(as.character(substitute(month)))
  month <- paste0(toupper(substr(month, 1, 1)), 
                  substr(month, 2, nchar(month)))
  if (month %in% month.abb) month <- month.name[match(month, month.abb)]
  getRate(month)
}    

getRate2(AUG)
# [1] 0.16
getRate2(Aug)
# [1] 0.16
getRate2(AugUST)
# [1] 0.16
getRate2("aug")
# [1] 0.16

不能 return 基于参数的数据框中的值

Can't return a value from dataframe based on parameter

lookup

r

function