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法律学如何根据第一个字符从 R 中的字符串向量中提取字符串？
有时，向量字符串具有模式，而有时我们需要根据字符从字符串向量中创建模式。例如，我们可能希望从包含所有名称的向量中提取美国各州的名称。这可通过使用 grepl 函数来完成。
示例
考虑下面包含美国各州名称的向量-
> US_states<-c("Alabama", "Alaska", "American Samoa", "Arizona", "Arkansas",
"California", "Colorado", "Connecticut", "Delaware", "District of Columbia", "Florida",
"Georgia", "Guam", "Hawaii", "Idaho", "Illinois", "Indiana", "Iowa", "Kansas",
"Kentucky", "Louisiana", "Maine", "Maryland", "Massachusetts", "Michigan",
"Minnesota", "Minor Outlying Islands", "Mississippi", "Missouri", "Montana",
"Nebraska", "Nevada", "New Hampshire", "New Jersey", "New Mexico", "New York",
"North Carolina", "North Dakota", "Northern Mariana Islands", "Ohio", "Oklahoma",
"Oregon", "Pennsylvania", "Puerto Rico", "Rhode Island", "South Carolina", "South
Dakota", "Tennessee", "Texas", "U.S. Virgin Islands", "Utah", "Vermont", "Virginia",
"Washington", "West Virginia", "Wisconsin", "Wyoming")
> US_states[grepl("^A",US_states)]
[1] "Alabama" "Alaska" "American Samoa" "Arizona"
[5] "Arkansas"
> US_states[grepl("^B",US_states)]
character(0)
> US_states[grepl("^C",US_states)]
[1] "California" "Colorado" "Connecticut"
> US_states[grepl("^D",US_states)]
[1] "Delaware" "District of Columbia"
> US_states[grepl("^E",US_states)]
character(0)
> US_states[grepl("^F",US_states)]
[1] "Florida"
> US_states[grepl("^G",US_states)]
[1] "Georgia" "Guam"
> US_states[grepl("^H",US_states)]
[1] "Hawaii"
> US_states[grepl("^I",US_states)]
[1] "Idaho" "Illinois" "Indiana" "Iowa"
> US_states[grepl("^J",US_states)]
character(0)
> US_states[grepl("^K",US_states)]
[1] "Kansas" "Kentucky"
> US_states[grepl("^L",US_states)]
[1] "Louisiana"
> US_states[grepl("^M",US_states)]
[1] "Maine" "Maryland" "Massachusetts"
[4] "Michigan" "Minnesota" "Minor Outlying Islands"
[7] "Mississippi" "Missouri" "Montana"
> US_states[grepl("^N",US_states)]
[1] "Nebraska" "Nevada"
[3] "New Hampshire" "New Jersey"
[5] "New Mexico" "New York"
[7] "North Carolina" "North Dakota"
[9] "Northern Mariana Islands"
> US_states[grepl("^O",US_states)]
[1] "Ohio" "Oklahoma" "Oregon"
> US_states[grepl("^P",US_states)]
[1] "Pennsylvania" "Puerto Rico"
> US_states[grepl("^Q",US_states)]
character(0)
> US_states[grepl("^R",US_states)]
[1] "Rhode Island"
> US_states[grepl("^S",US_states)]
[1] "South Carolina" "South Dakota"
> US_states[grepl("^T",US_states)]
[1] "Tennessee" "Texas"
> US_states[grepl("^U",US_states)]
[1] "U.S. Virgin Islands" "Utah"
> US_states[grepl("^V",US_states)]
[1] "Vermont" "Virginia"
> US_states[grepl("^W",US_states)]
[1] "Washington" "West Virginia" "Wisconsin" "Wyoming"
> US_states[grepl("^X",US_states)]
character(0)
> US_states[grepl("^Y",US_states)]
character(0)
> US_states[grepl("^Z",US_states)]
character(0)
更新日期： 2020 年 09 月 04 日
283 次浏览
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