有没有一种方法可以同时对多个变量进行重新编码？

Question

我有一个从D到A+的学生成绩单标记的数据集。我想把它们重新计算为1-12 (即D- = 1，D=2.A= 11，A+ = 12)。现在我正在起诉revalue函数在plyr中。我有几个列要重新编码--是否有比在每一列上运行revalue更短的方法？

一些数据：

student  <- c("StudentA","StudentB","StudentC","StudentD","StudentE","StudentF","StudentG","StudentH","StudentI","StudentJ")
read <- c("A", "A+", "B", "B-", "A", "C", "C+", "D", "C", "B+")
write <- c("A-", "B", "C", "C+", "D", "B-", "B", "C", "D+", "B")
math <- c("C", "C", "D+", "A", "A+", "B", "B-", "C-", "D+", "C")

df <- data.frame (student, read, write, math)

现在我给他们做了这样的记录：

df$read.r <- as.numeric (revalue (df$read, c("D-" = "1",
                             "D" = "2",
                             "D+" = "3",
                             "C-" = "4",
                             "C" = "5",
                             "C+" = "6",
                             "B-" = "7",
                             "B" = "8",
                             "B+" = "9",
                             "A-" = "10",
                             "A" = "11",
                             "A+" = "12"
                             )))

与其运行这3次(或更多)，还有更好的方法吗？所有的列都有相同的值。

Answer 1

 df1 <- df[,-1]

df1[] <- as.numeric(factor(unlist(df[,-1]), 
         levels=paste0(rep(LETTERS[4:1], each=3), c("-", "", "+"))))
cbind(df, setNames(df1, paste(colnames(df1), "r", sep=".")))
#       student read write math read.r write.r math.r
#1  StudentA    A    A-    C     11      10      5
#2  StudentB   A+     B    C     12       8      5
#3  StudentC    B     C   D+      8       5      3
#4  StudentD   B-    C+    A      7       6     11
#5  StudentE    A     D   A+     11       2     12
#6  StudentF    C    B-    B      5       7      8
#7  StudentG   C+     B   B-      6       8      7
#8  StudentH    D     C   C-      2       5      4
#9  StudentI    C    D+   D+      5       3      3
#10 StudentJ   B+     B    C      9       8      5

Answer 2

您可以使用match()。首先，把所有的分数放在一个向量中，从最差到最好。

marks <- c("D-", "D", "D+", "C-", "C", "C+", "B-", "B", "B+", "A-", "A", "A+")。

然后

df$read.mark <- match(df$read, marks)

为了避免编写三次，只需将其放入一个函数中，或者使用apply() (如apply(df[2:4], 2, match, marks) )按列进行应用。

Answer 3

不是超级高效，但至少可以解决你的3x问题：

df[,2:4] <- revalue(as.matrix(df[,2:4]), c("B"=9))