使用R中的stringr提取变量名称

Question

我试图从以下向量中提取一些变量名称和数字，并将它们存储到两个新变量中：

unique_strings <- c("PM_1_PMS5003_S_Avg", "PM_2_5_PMS5003_S_Avg", "PM_10_PMS5003_S_Avg", 
  "PM_1_PMS5003_A_Avg", "PM_2_5_PMS5003_A_Avg", "PM_10_PMS5003_A_Avg", 
  "PNC_0_3_PMS5003_Avg", "PNC_0_5_PMS5003_Avg", "PNC_1_0_PMS5003_Avg", 
  "PNC_2_5_PMS5003_Avg", "PNC_5_0_PMS5003_Avg", "PNC_10_0_PMS5003_Avg", 
  "PM_1_PMS7003_S_Avg", "PM_2_5_PMS7003_S_Avg", "PM_10_PMS7003_S_Avg", 
  "PM_1_PMS7003_A_Avg", "PM_2_5_PMS7003_A_Avg", "PM_10_PMS7003_A_Avg", 
  "PNC_0_3_PMS7003_Avg", "PNC_0_5_PMS7003_Avg", "PNC_1_0_PMS7003_Avg", 
  "PNC_2_5_PMS7003_Avg", "PNC_5_0_PMS7003_Avg", "PNC_10_0_PMS7003_Avg"
)

我想在PMS之前提取每个字符作为第一个变量。这包括与PM或PNC一起使用的字符串，以及下划线和数字。我想将这些结果存储到一个名为pollutant的变量中。

期望的输出：

unique(pollutant)
[1] "PM_1" "PM_2_5" "PM_10" "PNC_0_3" "PNC_0_5" "PNC_1_0" "PNC_2_5" "PNC_5_0" "PNC_10"

我想在PMS之后为第二个变量提取所有内容。

为此，我首先尝试从每个字符串中提取模型编号（以003结尾的四位数字），但是，在提取中包含A_Avg或S_Avg也很有用。

这是我的第一次尝试：

model_id <- str_extract(unique_strings, "[0-9]{4,}")

unique(model_id)
[1] "5003" "7003"

我以前没有使用正则表达式，并且很难在现有的docs / stack帖子中导航。感谢您的意见！

Answer 1

我们可以使用str_split来分割基于"PMS"的字符串。之后，使用str_replace删除第一列中的最后一个"_"。输出是m。第一个变量位于第一列，而第二个变量位于第二列。

library(stringr)
m <- str_split(unique_strings, pattern = "PMS", simplify = TRUE)
m[, 1] <- str_replace(m[, 1], "_$", "")
m
#       [,1]       [,2]        
#  [1,] "PM_1"     "5003_S_Avg"
#  [2,] "PM_2_5"   "5003_S_Avg"
#  [3,] "PM_10"    "5003_S_Avg"
#  [4,] "PM_1"     "5003_A_Avg"
#  [5,] "PM_2_5"   "5003_A_Avg"
#  [6,] "PM_10"    "5003_A_Avg"
#  [7,] "PNC_0_3"  "5003_Avg"  
#  [8,] "PNC_0_5"  "5003_Avg"  
#  [9,] "PNC_1_0"  "5003_Avg"  
# [10,] "PNC_2_5"  "5003_Avg"  
# [11,] "PNC_5_0"  "5003_Avg"  
# [12,] "PNC_10_0" "5003_Avg"  
# [13,] "PM_1"     "7003_S_Avg"
# [14,] "PM_2_5"   "7003_S_Avg"
# [15,] "PM_10"    "7003_S_Avg"
# [16,] "PM_1"     "7003_A_Avg"
# [17,] "PM_2_5"   "7003_A_Avg"
# [18,] "PM_10"    "7003_A_Avg"
# [19,] "PNC_0_3"  "7003_Avg"  
# [20,] "PNC_0_5"  "7003_Avg"  
# [21,] "PNC_1_0"  "7003_Avg"  
# [22,] "PNC_2_5"  "7003_Avg"  
# [23,] "PNC_5_0"  "7003_Avg"  
# [24,] "PNC_10_0" "7003_Avg"

Answer 2

我们可以使用str_extract从字符串（^）的开头（^(PM|PNC)）跟随'PM'或'PNC'，然后是_和一个或多个数字（\\d+），然后是具有另一组_和数字的情况（为此我们指定零或更多（(_\\d)*）

library(stringr)
out <- str_extract(unique_strings, "^(PM|PNC)_\\d+(_\\d)*")

这将为那些没有匹配的元素提供NA。如果我们需要删除那些

na.omit(out)

---

对于第二种情况，尚不清楚所需的输出。如果我们需要在PMS之后提取所有内容，我们可以使用regexlookbehind（(?<=PMS)）并匹配后面的所有字符（.*）

str_extract(unique_strings, "(?<=PMS).*")