R 基于数据子集创建新的分类变量

我有一个如下所示的数据帧：

         cnt    bnk qst ans
1  Country 1 Bank 1  q1   1
2  Country 2 Bank 2  q1   1
3  Country 3 Bank 3  q1   3
4  Country 4 Bank 4  q1   1
5  Country 1 Bank 1  q2   1
6  Country 2 Bank 2  q2   2
7  Country 3 Bank 3  q2   3
8  Country 4 Bank 4  q2   4
9  Country 1 Bank 1  q3   1
10 Country 2 Bank 2  q3   1
11 Country 3 Bank 3  q3   2
12 Country 4 Bank 4  q3   1

         cnt    bnk qst ans   dummy
1  Country 1 Bank 1  q1   1  Public
2  Country 2 Bank 2  q1   1 Private
3  Country 3 Bank 3  q1   3   Mixed
4  Country 4 Bank 4  q1   1  Other'
5  Country 1 Bank 1  q2   1  Public
6  Country 2 Bank 2  q2   2 Private
7  Country 3 Bank 3  q2   3   Mixed
8  Country 4 Bank 4  q2   4  Other'
9  Country 1 Bank 1  q3   1  Public
10 Country 2 Bank 2  q3   1 Private
11 Country 3 Bank 3  q3   2   Mixed
12 Country 4 Bank 4  q3   1  Other'

请参考，

q

代表“问题”。因此，

q2

是“问题2”。类似地，

ans

是响应

现在，我想根据

q2

中的响应创建一个分类变量。我特别想指定以下类别：

公开的

私人的

混合的

其他

因此，如果

ans=1

到

qst=q2

，这是“公共的”；如果

ans=2

到

qst=q2

这是“私有的”，等等。因此，这之后的数据帧应该如下所示：

         cnt    bnk qst ans
1  Country 1 Bank 1  q1   1
2  Country 2 Bank 2  q1   1
3  Country 3 Bank 3  q1   3
4  Country 4 Bank 4  q1   1
5  Country 1 Bank 1  q2   1
6  Country 2 Bank 2  q2   2
7  Country 3 Bank 3  q2   3
8  Country 4 Bank 4  q2   4
9  Country 1 Bank 1  q3   1
10 Country 2 Bank 2  q3   1
11 Country 3 Bank 3  q3   2
12 Country 4 Bank 4  q3   1

         cnt    bnk qst ans   dummy
1  Country 1 Bank 1  q1   1  Public
2  Country 2 Bank 2  q1   1 Private
3  Country 3 Bank 3  q1   3   Mixed
4  Country 4 Bank 4  q1   1  Other'
5  Country 1 Bank 1  q2   1  Public
6  Country 2 Bank 2  q2   2 Private
7  Country 3 Bank 3  q2   3   Mixed
8  Country 4 Bank 4  q2   4  Other'
9  Country 1 Bank 1  q3   1  Public
10 Country 2 Bank 2  q3   1 Private
11 Country 3 Bank 3  q3   2   Mixed
12 Country 4 Bank 4  q3   1  Other'

我试图使用ifelse，但我没能做到我想做的。有人能给我一些建议吗

数据

dput(df)
structure(list(cnt = c("Country 1", "Country 2", "Country 3", 
"Country 4", "Country 1", "Country 2", "Country 3", "Country 4", 
"Country 1", "Country 2", "Country 3", "Country 4"), bnk = c("Bank 1", 
"Bank 2", "Bank 3", "Bank 4", "Bank 1", "Bank 2", "Bank 3", "Bank 4", 
"Bank 1", "Bank 2", "Bank 3", "Bank 4"), qst = structure(c(1L, 
1L, 1L, 1L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L), .Label = c("q1", 
"q2", "q3"), class = "factor"), ans = c(1L, 1L, 3L, 1L, 1L, 2L, 
3L, 4L, 1L, 1L, 2L, 1L), dummy = c(NA, NA, NA, NA, "Public", 
"Private", "Mixed", "Other", NA, NA, NA, NA)), .Names = c("cnt", 
"bnk", "qst", "ans", "dummy"), row.names = c("1", "2", "3", "4", 
"5", "6", "7", "8", "9", "10", "11", "12"), class = "data.frame")

---

以下内容将为所有其他Qs设置

NA

df$dummy <- ifelse(df$ans == 1 & df$qst == 'q2', 'Public', 
               ifelse(df$ans == 2 & df$qst == 'q2', 'Private', 
                   ifelse(df$ans == 3 & df$qst == 'q2', 'Mixed', 
                        ifelse(df$ans == 4 & df$qst == 'q2', 'Other', NA))))

#         cnt    bnk qst ans   dummy
#1  Country 1 Bank 1  q1   1    <NA>
#2  Country 2 Bank 2  q1   1    <NA>
#3  Country 3 Bank 3  q1   3    <NA>
#4  Country 4 Bank 4  q1   1    <NA>
#5  Country 1 Bank 1  q2   1  Public
#6  Country 2 Bank 2  q2   2 Private
#7  Country 3 Bank 3  q2   3   Mixed
#8  Country 4 Bank 4  q2   4   Other
#9  Country 1 Bank 1  q3   1    <NA>
#10 Country 2 Bank 2  q3   1    <NA>
#11 Country 3 Bank 3  q3   2    <NA>
#12 Country 4 Bank 4  q3   1    <NA>

---

df$dummy对于名为df的data.frame，下面类似的内容将起作用。如果没有数据，很难进行测试：

# construct dummy variable in subset data.frame
dfCountryQ2 <- df[df$qst=="q2", c("cnt", "ans")]
dfCountryQ2$dummy <- factor(dfCountryQ2$ans, levels=1:4,
                            labels=c("Public", "Private", "Mixed", "Other"))

# merge on by country
df <- merge(df, dfCountryQ2[, c("cnt", "dummy")], by="cnt")

#在subset data.frame中构造虚拟变量
dfCountryQ2第二个条目是
Private
但是
ans=1
是，因为我不关心
q1
的
ans
，而是关于
q2
。