在R中：如何根據現有變量的條件創建新變量

Question

在R中，我想根據我應用於現有變量（var1和var2）的條件創建兩個新變量（var3和var4），這些變量具有重復記錄。 這是我的數據的樣子。

Var1  var2  
01     A
01     B
01     A
02     C
02     C
03     D
04     E
04     D
04     F
.      .
.      .
.      .
.      .
.      .

我會在SAS中使用以下if-else-then語句。

if var1 = 01 and var2 = "A" then do; var3 = "New York"; var4= "Buffalo"; end; else;
if var1 = 01 and var2 = "B" then do; var3 = "New York"; var4= "Cornell"; end; else;
if var1 = 02 and var2 = "C" then do; var3 = "North Carolina"; var4= "Raleigh"; end; else;
if var1 = 03 and var = "D"then do; var3 = "Texas"; var4= "Dallas"; end; else;

我的輸出將如下所示

Var1  var2    var3             var4
01     A      New York         Buffalo
01     B      New York         Cornell
01     A      New York         Buffalo
02     C      North Carolina   Raleigh
02     C      North Carolina   Raleigh
03     D      Texas            Dallas
.      .      .                 .
.      .      .                 . 
.      .      .                 .
.      .      .                 .    

任何有助於在R中創建上述輸出的幫助都非常感謝。 我是否需要使用if-else和for statement，ifelse等？

Answer 1

df$var3<-ifelse(Var1==01, "New York",
         ifelse(Var1==02, "North Carolina",
         ifelse(Var1==03, "Texas", NA)))
df$var4<-....

或者通過申請標簽：

df$var3<-factor(df$Var1,
                levels = 1:3,
                labels = c("New York","North Carolina","Texas"))

Answer 2

您可以創建索引數據集（'df2'）並將其與原始數據集（'df1'）合並

 merge(df1, df2)
 #  var1 var2           var3    var4
 #1   01    A       New York Buffalo
 #2   01    A       New York Buffalo
 #3   01    B       New York Cornell
 #4   02    C North Carolina Raleigh
 #5   02    C North Carolina Raleigh
 #6   03    D          Texas  Dallas

數據

df1 <- structure(list(var1 = c("01", "01", "01", "02", "02", "03"), 
var2 = c("A", "B", "A", "C", "C", "D")), .Names = c("var1", 
"var2"), row.names = c(NA, -6L), class = "data.frame")

df2 <-  data.frame(var1=c('01', '01', '02', '03'), var2=LETTERS[1:4], 
 var3=c('New York', 'New York', 'North Carolina', 'Texas'),
 var4=c('Buffalo', 'Cornell', 'Raleigh', 'Dallas'))