Question

我有一个包含102行的数据框，我需要使用if语句开发一个for循环，以根据其他列（Sp，Su，Fa，Wi）填充新列“Season”。我有一个“1”填充样本发生的季节（见下文）。

Sp  Su  Fa  Wi
1   0   0   0
0   0   0   1

我试着在夏天做一个循环，但是我遇到了很多错误。我似乎无法掌握For和if循环。我们将不胜感激。

for(i in 1:102) {  if(myData$Su==1) myData$Season=Summer}

错误：

In if (myData$Su == 1) myData$Season = Summer :
  the condition has length > 1 and only the first element will be used

Answer 1

尝试识别哪个列有1，然后使用此索引从char向量返回季节的名称：

data <- c("Sp  Su  Fa  Wi
           1   0   0   0
           0   0   0   1")
data <- read.table(text=data,header=TRUE)

data$Season <- c("Spring","Summer","Fall","Winter")[which(data==1,arr.ind=TRUE)[,"col"]]

结果：

  Sp Su Fa Wi Season
1  1  0  0  0 Spring
2  0  0  0  1 Winter

Answer 2

由于R是基于矢量的语言，因此在这种情况下不需要for循环。

dat <- data.frame(
  Sp = c(1, 0),
  Su = c(0, 0),
  Fa = c(0, 0),
  Wi = c(0, 1)
)

一种天真的，蛮力的方式是使用嵌套的ifelse()函数：

dat$Season <- with(dat, 
                   ifelse(Sp == 1, "Spring", 
                          ifelse(Su == 1, "Summer", 
                                 ifelse(Fa == 1, "Fall", 
                                        "Winter"))))
dat

  Sp Su Fa Wi Season
1  1  0  0  0 Spring
2  0  0  0  1 Winter

但R方式是考虑数据的结构，然后使用索引，例如：

dat$season <- apply(dat, 1, function(x) c("Sp", "Su", "Fa", "Wi")[x==1])

  Sp Su Fa Wi season
1  1  0  0  0     Sp
2  0  0  0  1     Wi

Answer 3

ifelse(myData$Su==1, myData$Season=="Summer",myData$Season=="Not Summer")

或更复杂的“否”声明（例如嵌套ifelse - 如果Wi == 1，设置为冬季等）

Answer 4

如果你真的想要使用循环，你应该这样做：

# recreating an example similar to your data
myData <- read.csv(text= 
"Sp,Su,Fa,Wi
1,0,0,0
0,1,0,0
0,0,1,0
1,0,0,0
0,0,0,1")

# before the loop, add a new "Season" column to myData filled with NAs
myData$Season <- NA

# don't use 102 but nrow(myData) so
# in case myData changes you don't have to modify the code
for(i in 1:nrow(myData)){

  # here you are working row-by-row
  # so note the [i] indexing below

  if(myData$Sp[i] == 1){
    myData$Season[i] = "Spring"
  }else if(myData$Su[i] == 1){
    myData$Season[i] = "Summer"
  }else if(myData$Fa[i] == 1){
    myData$Season[i] = "Fall"
  }else if(myData$Wi[i] == 1){
    myData$Season[i] = "Winter"
  }
}

但实际上（如其他答案所示）有更有效和更快捷的方式。

Answer 5

您也可以使用（@ Emer＆＃39的方法）

 transform(dat, Season=c('Spring', 'Summer', 'Fall',
             'Winter')[as.matrix(seq_len(ncol(dat))*dat)])
 #  Sp Su Fa Wi Season
 #1  1  0  0  0 Spring
 #2  0  0  0  1 Winter

数据

 dat <- structure(list(Sp = c(1, 0), Su = c(0, 0), Fa = c(0, 0), Wi = c(0, 
 1)), .Names = c("Sp", "Su", "Fa", "Wi"), row.names = c(NA, -2L
 ), class = "data.frame")

如何使用for循环和if语句在数据框中创建新列

5 个答案:

数据