R：使用所需子字符串列表清理字符串

Question

我有一个带有字符串的数据框

Clause <- c('Big Truck Pb Anomaly Low', 'Red Truck Fe Anomaly High', 'Blue Truck Pb Anomaly High & Old Truck Fe Anomaly Low')
Input <- data.frame(Clause)

我想通过仅保留在清理列表中找到的子字符串来清理该字符串；

Keepers <- c('Anomaly', 'Low', 'High', '&', 'Pb', 'Fe', ' ', 'SomethingNotPresent')

想要的结果如下。

Wanted <- c('Pb Anomaly Low', 'Fe Anomaly High', 'Pb Anomaly High & Fe Anomaly Low')
Result <- data.frame(Wanted)

注意：'Keepers' 列表还将包含 'SomethingNotPresent'

等项目

Answer 1

您可以形成白名单条款的正则表达式替换以保留。然后使用否定前瞻模式来识别所有应该删除的 terms/whitespace：

alternation <- paste(Keepers, collapse="|")
regex <- paste0("\s*(?!(?:", alternation, "))(?<!\S)\S+(?!\S)\s*")
df$clause <- gsub("\s+", " ", trimws(gsub(regex, " ", df$clause, perl=TRUE)))
df

                            clause
1                   Pb Anomaly Low
2                  Fe Anomaly High
3 Pb Anomaly High & Fe Anomaly Low

数据：

inp <- c('Big Truck Pb Anomaly Low', 'Red Truck Fe Anomaly High',
         'Blue Truck Pb Anomaly High & Old Truck Fe Anomaly Low')
df <- data.frame(clause=inp, stringsAsFactors=FALSE)
Keepers <- c('Anomaly', 'Low', 'High', '&', 'Pb', 'Fe', ' ', 'SomethingNotPresent')

Answer 2

您可以在每个单词处拆分字符串，每行仅保留 Keepers 个单词。

sapply(strsplit(Input$Clause, '\s+'), function(x) 
       paste0(x[x %in% Keepers], collapse = ' '))

#[1] "Pb Anomaly Low"     "Fe Anomaly High"     "Anomaly High & Fe Anomaly Low"

R：使用所需子字符串列表清理字符串

R: Cleaning a string using a list of wanted substrings

string

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data-cleaning