如何用ifelse()修改数据框列值？遇返回FALSE而非52的问题

我尝试用ifelse()修改数据框的week列值：当month为'January'且day为31时，将week改为52，但结果中本该显示52的位置却出现了FALSE。示例如下：

> a
   SampleDate year   month week day
1  2013-01-05 2013 January   01  05
2  2013-01-08 2013 January   02  08
3  2013-01-08 2013 January   02  08
4  2013-01-05 2013 January   01  05
5  2013-01-05 2013 January   01  05
6  2013-01-08 2013 January   02  08
7  2013-01-08 2013 January   02  08
8  2013-01-05 2013 January   01  05
9  2013-01-03 2013 January   01  03
10 2013-01-08 2013 January   02  08
11 2013-01-07 2013 January   02  07
12 2013-01-03 2013 January   01  03
13 2013-01-03 2013 January   01  03
14 2013-01-08 2013 January   02  31
15 2013-01-07 2013 January   02  07
16 2013-01-03 2013 January   01  31
> 
> ## "FALSE" should be 52
> with(a, ifelse(month == 'January' & day == 31, week == 52, week))
 [1] "01"    "02"    "02"    "01"    "01"    "02"    "02"    "01"    "01"   
[10] "02"    "02"    "01"    "01"    "FALSE" "02"    "FALSE"

数据 #

a <- structure(list(SampleDate = structure(c(15710, 15713, 15713, 
15710, 15710, 15713, 15713, 15710, 15708, 15713, 15712, 15708, 
15708, 15713, 15712, 15708), class = "Date"), year = c("2013", 
"2013", "2013", "2013", "2013", "2013", "2013", "2013", "2013", 
"2013", "2013", "2013", "2013", "2013", "2013", "2013"), month = c("January", 
"January", "January", "January", "January", "January", "January", 
"January", "January", "January", "January", "January", "January", 
"January", "January", "January"), week = c("01", "02", "02", 
"01", "01", "02", "02", "01", "01", "02", "02", "01", "01", "02", 
"02", "01"), day = c("05", "08", "08", "05", "05", "08", "08", 
"05", "03", "08", "07", "03", "03", "31", "07", "31")), row.names = c(NA, 
-16L), class = "data.frame")

解决方法 #

错误原因 #

你在ifelse的第二个参数中写了week == 52，这是一个比较运算，会返回布尔值TRUE或FALSE，而不是将week赋值为52。另外你的day列是字符型，判断时最好用字符值'31'保持类型一致。

正确代码 #

with(a, ifelse(month == 'January' & day == '31', "52", week))

运行结果 #

[1] "01" "02" "02" "01" "01" "02" "02" "01" "01" "02" "02" "01" "01" "52" "02" "52"

内容的提问来源于stack exchange，提问作者Salvador