Question

我现在正在Coursera上做R编程入门课程，我的代码中有以下疑问。以下是我的代码。

 rankall <- function(outcome, num = "best") {

  ## Read outcome data
  dat <- read.csv("outcome-of-care-measures.csv")





## Check that outcome are valid
  outcomeValues <- c("heart attack", "heart failure", "pneumonia")

  if(!(outcome %in% outcomeValues)){
    stop("invalid outcome")


    }

  column <- if(outcome == "heart attack"){
    11
  }
  else if(outcome == "heart failure"){
    17
  }
  else if(outcome == "pneumonia") {
    23
  }

  dat[, column] <- suppressWarnings(as.numeric(levels(dat[, column])[dat[, column]]))
  dat[, 2] <- as.character(dat[, 2])
  dat[, 11] <- as.numeric(dat[, 11]) # heart attack
  dat[, 17] <- as.numeric(dat[, 17]) # heart failure
  dat[, 23] <- as.numeric(dat[, 23]) # pneumonia
  output <- vector()
  states <- levels(dat[, 7])

  ## Return hospital name in that state with lowest 30-day death rate
  ## For each state, find the hospital of the given rank
  for( i in 1:length(states)){




 stateData <- dat[grep(states[i], dat$State), ]
  outcomeData <- stateData[order(stateData[, column], stateData[, 2], na.last = NA), ]
  hospital <- if(num == "best" || num == 1){
    outcomeData[1, 2]
  }
  else if(num == "worst") {
    outcomeData[nrow(outcomeData), 2]
  }
  else {
    outcomeData[num, 2]
  }
  result <- append(result, c(hospital, states[i]))
  }




## Return a data frame with the hospital names and the (abbreviated) state name
  result <- as.data.frame(matrix(result, nrow = length(states), ncol = 2, byrow = TRUE))
  colnames(result) <- c("Hospital names", "State")


  result
  }

在上面的代码中，如果我替换 states <- levels(dat[, 7]) states <- unique(dat[,7])，我没有得到正确的输出。我不明白为什么。

而且，如果我取下

dat[, column] <- suppressWarnings(as.numeric(levels(dat[, column])[dat[, column]]))

我的代码没有生成正确的输出。我试过提取抑制警告文件，但要么我错过了某个地方，要么我无法在任何地方找到正确的答案。

Answer 1

因为因子列可能具有比实际值更多的级别，例如：

x <- factor(1:3, levels = 1:4)
x
# [1] 1 2 3
# Levels: 1 2 3 4

unique(x)
# [1] 1 2 3
# Levels: 1 2 3 4
length(unique(x))
# [1] 3

levels(x)
# [1] "1" "2" "3" "4"
length(levels(x))
# [1] 4

当我们稍后想要将值“4”添加到x时，这很有用。

独特和级别之间的差异以及抑制警告的使用

1 个答案: