设置数据子集将丢失我的所有观察结果

Question

我有一个数据帧“测试”，我希望子集，但当我尝试时，我失去了所有的观测值。为什么会发生这种情况？

> str(Test)
'data.frame':   157025 obs. of  13 variables:
$ Cancellations    : int  1 1 1 1 1 1 1 1 1 1 ...
$ Benefit          : chr  "Single Parent Support                          "               "Single Parent Support                          " "Job Seeker                                         " "Job Seeker                                     " ...
$ Region           : chr  "        Northland    " "        Northland    " "            Northland    " "        Northland    " ...
$ Month            : chr  "Jun 14" "Jun 14" "Jun 14" "Jun 14" ...
$ CanReason        : chr  "Change in Marital Status           " "Change in     Marital Status           " "Change in Marital Status           " "Change in     Marital Status           " ...
$ Age              : chr  " 20-24 " " 20-24 " " 20-24 " " 20-24 " ...
$ Ethnicity        : chr  "NZ European/Pakeha" "Maori             " "Other                      " "NZ European/Pakeha" ...
$ SMS              : chr  "General Case Management               " "Work     Focused Case Management          " "Work Focused Case Management          " "Work     Search Support                   " ...
$ Duration         : chr  "2-4 yrs " "2-4 yrs " "6-9 mth " "0-3 mth " ...
$ SMSDuration      : int  361 348 59 69 150 37 63 294 107 107 ...
$ AgeYoungest      : chr  "0-4 yrs    " "0-4 yrs    " "No Children" "No    Children" ...
$ AgeYoungestNonSub: chr  "0-4 yrs" "0-4 yrs" "No Children" "No Children" ...
$ Liability        : chr  " 166,000 " " 166,000 " " 102,000 " " 102,000 " ...


> subDie <- Test[CanReason == "Died",]

> str(subDie)
'data.frame':   0 obs. of  13 variables:
$ Cancellations    : int 
$ Benefit          : chr 
$ Region           : chr 
$ Month            : chr 
$ CanReason        : chr 
$ Age              : chr 
$ Ethnicity        : chr 
$ SMS              : chr 
$ Duration         : chr 
$ SMSDuration      : int 
$ AgeYoungest      : chr 
$ AgeYoungestNonSub: chr 
$ Liability        : chr 

我尝试过将因子变量转换为字符。当我将逗号放在" CanReason“索引行(subDie <- Test，CanReason == "Died")的前面时，R告诉我在0个变量上有157025个观察值……我被难住了

Answer 1

使用正则表达式在字符矢量CanReason中搜索字符串"Died"，使用grepl()返回指示匹配与否的逻辑矢量。使用它来对Test进行子集。

例如

set.seed(12)
CanReason <- sample(c("Change in      Marital status",
                      "Change in   Marital status ",
                      " Died    ",
                      "Died                ",
                      "Died"), 10000, replace = TRUE)
ind <- grepl("Died", CanReason)

sum(ind)
length(CanReason[ind])

给予：

> sum(ind)
[1] 6037
> length(CanReason[ind])
[1] 6037
> head(CanReason[ind])
[1] "Died"                 "Died"                 "Died                "
[4] "Died"                 " Died    "            " Died    "