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法律學如何根據第一個字元從 R 中的字串向量中提取字串？
有時，向量字串具有模式，而有時我們需要根據字元從字串向量中建立模式。例如，我們可能希望從包含所有名稱的向量中提取美國各州的名稱。這可透過使用 grepl 函式來完成。
示例
考慮下面包含美國各州名稱的向量-
> 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 次瀏覽
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