如何計算 R 數據框中字符串中“c(\”) 的出現次數？

Question

我有一個數據框，其中某些列包含來自 Mplus 的錯誤和警告消息。 文本以一種奇怪的格式保存，因此我希望通過計算單元格中 c(\ 的出現次數來簡單地計算消息的數量，而不是嘗試處理每條消息，因為它是出現在每個消息之前的唯一字符組合警告或錯誤。

例如，一個單元格包含以下消息：

[[1]]
[1] "c(\"All variables are uncorrelated with all other variables within class.\""
[2] " \"Check that this is what is intended.\""                                  
[3] " \"1 WARNING(S) FOUND IN THE INPUT INSTRUCTIONS\")"                         
[4] " c(\"WARNING:  THE BEST LOGLIKELIHOOD VALUE WAS NOT REPLICATED.  THE\""     
[5] " \"SOLUTION MAY NOT BE TRUSTWORTHY DUE TO LOCAL MAXIMA.  INCREASE THE\""    
[6] " \"NUMBER OF RANDOM STARTS.\")" 

而另一個包含一個較短的消息，如下所示：

[[1]]
[1] "c(\"All variables are uncorrelated with all other variables within class.\""
[2] " \"Check that this is what is intended.\""                                  
[3] " \"1 WARNING(S) FOUND IN THE INPUT INSTRUCTIONS\")" 

我嘗試使用 str_count 幾種不同的方式，包括我最近的嘗試：

    str_count(test#, '//c(\//')

但我收到錯誤： Error: '\/' is an unrecognized escape in character string starting "'//c(\/" 。理想情況下，第一個示例返回 2，第二個示例返回 1。

當這個唯一字符串包含大多數封裝它或 escaping 的字符時，我如何計算它的出現次數？

這里有一些易於使用的測試代碼來試一試！

test1 <- '"c(\"All variables are uncorrelated with all other variables within class.\"" " \"Check that this is what is intended.\"" " \"1 WARNING(S) FOUND IN THE INPUT INSTRUCTIONS\")"'

test2 <- '"c(\"All variables are uncorrelated with all other variables within class.\"" " \"Check that this is what is intended.\"" " \"1 WARNING(S) FOUND IN THE INPUT INSTRUCTIONS\")"'

Answer 1

您可以嘗試在我的評論中減少要計算的部分

str_count(test1, "c\\(")

或者您可以通過檢查c(\"來延長參數並使用 fixed() 參數：

str_count(test1, fixed('c(\"'))

Answer 2

你可以試試gregexpr() 。

test1 <- '"c(\" foo bar baz'
test2 <- '"c(\" foo bar baz "c(\" baz bar foo'

length(unlist(gregexpr('c\\(', test1)))
# [1] 1
length(unlist(gregexpr('c\\(', test2)))
# [1] 2
length(unlist(gregexpr('c\\(', list(test1, test2))))
# [1] 3