为了在 R 中提取最多固定数量字符的字符串向量元素，我们可以使用基 R 的子字符串函数。
例如，如果我们有一个字符串向量，比如包含 100 个字符串值的 X，并且我们想要找到每个值的前五个字符，那么我们可以使用下面给出的命令 -
substring(X,1,5)
以下代码段创建了一个示例数据框 -
x1<-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")
x1创建了以下数据框
[1] "Alabama" "Alaska" [3] "American Samoa" "Arizona" [5] "Arkansas" "California" [7] "Colorado" "Connecticut" [9] "Delaware" "District of Columbia" [11] "Florida" "Georgia" [13] "Guam" "Hawaii" [15] "Idaho" "Illinois" [17] "Indiana" "Iowa" [19] "Kansas" "Kentucky" [21] "Louisiana" "Maine" [23] "Maryland" "Massachusetts" [25] "Michigan" "Minnesota" [27] "Minor Outlying Islands" "Mississippi" [29] "Missouri" "Montana" [31] "Nebraska" "Nevada" [33] "New Hampshire" "New Jersey" [35] "New Mexico" "New York" [37] "North Carolina" "North Dakota" [39] "Northern Mariana Islands" "Ohio" [41] "Oklahoma" "Oregon" [43] "Pennsylvania" "Puerto Rico" [45] "Rhode Island" "South Carolina" [47] "South Dakota" "Tennessee" [49] "Texas" "U.S. Virgin Islands" [51] "Utah" "Vermont" [53] "Virginia" "Washington" [55] "West Virginia" "Wisconsin" [57] "Wyoming"
要在上面创建的数据框中查找 x1 中每个值的前两个字符，请将以下代码添加到上面的代码段中 -
x1<-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")
substring(x1,1,2)输出结果如果您将上述所有给定的片段作为单个程序执行，它会生成以下输出 -
[1] "Al" "Al" "Am" "Ar" "Ar" "Ca" "Co" "Co" "De" "Di" "Fl" "Ge" "Gu" "Ha" "Id" [16] "Il" "In" "Io" "Ka" "Ke" "Lo" "Ma" "Ma" "Ma" "Mi" "Mi" "Mi" "Mi" "Mi" "Mo" [31] "Ne" "Ne" "Ne" "Ne" "Ne" "Ne" "No" "No" "No" "Oh" "Ok" "Or" "Pe" "Pu" "Rh" [46] "So" "So" "Te" "Te" "U." "Ut" "Ve" "Vi" "Wa" "We" "Wi" "Wy"
以下代码段创建了一个示例数据框 -
x2<-c("Austria", "Belgium", "Bulgaria", "Croatia", "Cyprus", "Czechia",
"Denmark", "Estonia", "Finland", "France", "Germany", "Greece", "Hungary",
"Ireland", "Italy", "Latvia", "Lithuania", "Luxembourg", "Malta",
"Netherlands", "Poland", "Portugal", "Romania", "Slovakia", "Slovenia",
"Spain", "Sweden")
x2创建了以下数据框
[1] "Austria" "Belgium" "Bulgaria" "Croatia" "Cyprus" [6] "Czechia" "Denmark" "Estonia" "Finland" "France" [11] "Germany" "Greece" "Hungary" "Ireland" "Italy" [16] "Latvia" "Lithuania" "Luxembourg" "Malta" "Netherlands" [21] "Poland" "Portugal" "Romania" "Slovakia" "Slovenia" [26] "Spain" "Sweden"
要在上面创建的数据框中找到 x2 中每个值的前两个字符，请将以下代码添加到上面的代码段中 -
x2<-c("Austria", "Belgium", "Bulgaria", "Croatia", "Cyprus", "Czechia",
"Denmark", "Estonia", "Finland", "France", "Germany", "Greece", "Hungary",
"Ireland", "Italy", "Latvia", "Lithuania", "Luxembourg", "Malta",
"Netherlands", "Poland", "Portugal", "Romania", "Slovakia", "Slovenia",
"Spain", "Sweden")
substring(x2,1,2)输出结果如果您将上述所有给定的片段作为单个程序执行，它会生成以下输出 -
[1] "Au" "Be" "Bu" "Cr" "Cy" "Cz" "De" "Es" "Fi" "Fr" "Ge" "Gr" "Hu" "Ir" "It" [16] "La" "Li" "Lu" "Ma" "Ne" "Po" "Po" "Ro" "Sl" "Sl" "Sp" "Sw"
以下代码段创建了一个示例数据框 -
x3<-c("Cuba", "Cyprus", "Czech Republic", "Djibouti", "Dominica", "Dominican
Republic", "East Timor", "Ecuador", "Egypt", "El Salvador", "Equatorial
Guinea", "Eritrea", "Estonia", "Ethiopia", "Fiji", "Finland", "France",
"Metropolitan", "French Guiana", "Gambia", "Georgia", "Germany", "Ghana",
"Greenland", "Grenada", "Guatemala", "Honduras", "Hong Kong", "Hungary",
"Iceland", "India", "Indonesia", "Iran", "Iraq", "Ireland", "Israel", "Italy",
"Jamaica", "Japan", "Jordan", "Kazakhstan", "Kenya", "Mozambique", "Namibia",
"Nepal", "Netherlands", "Nigeria", "Norway", "Oman", "Paraguay", "Peru",
"Philippines")
x3创建了以下数据框
[1] "Cuba" "Cyprus" "Czech Republic" [4] "Djibouti" "Dominica" "Dominican Republic" [7] "East Timor" "Ecuador" "Egypt" [10] "El Salvador" "Equatorial Guinea" "Eritrea" [13] "Estonia" "Ethiopia" "Fiji" [16] "Finland" "France" "Metropolitan" [19] "French Guiana" "Gambia" "Georgia" [22] "Germany" "Ghana" "Greenland" [25] "Grenada" "Guatemala" "Honduras" [28] "Hong Kong" "Hungary" "Iceland" [31] "India" "Indonesia" "Iran" [34] "Iraq" "Ireland" "Israel" [37] "Italy" "Jamaica" "Japan" [40] "Jordan" "Kazakhstan" "Kenya" [43] "Mozambique" "Namibia" "Nepal" [46] "Netherlands" "Nigeria" "Norway" [49] "Oman" "Paraguay" "Peru" [52] "Philippines"
要在上面创建的数据框中找到 x3 中每个值的前两个字符，请将以下代码添加到上面的代码段中 -
x3<-c("Cuba", "Cyprus", "Czech Republic", "Djibouti", "Dominica", "Dominican
Republic", "East Timor", "Ecuador", "Egypt", "El Salvador", "Equatorial
Guinea", "Eritrea", "Estonia", "Ethiopia", "Fiji", "Finland", "France",
"Metropolitan", "French Guiana", "Gambia", "Georgia", "Germany", "Ghana",
"Greenland", "Grenada", "Guatemala", "Honduras", "Hong Kong", "Hungary",
"Iceland", "India", "Indonesia", "Iran", "Iraq", "Ireland", "Israel", "Italy",
"Jamaica", "Japan", "Jordan", "Kazakhstan", "Kenya", "Mozambique", "Namibia",
"Nepal", "Netherlands", "Nigeria", "Norway", "Oman", "Paraguay", "Peru",
"Philippines")
substring(x3,1,2)输出结果如果您将上述所有给定的片段作为单个程序执行，它会生成以下输出 -
[1] "Cu" "Cy" "Cz" "Dj" "Do" "Do" "Ea" "Ec" "Eg" "El" "Eq" "Er" "Es" "Et" "Fi" [16] "Fi" "Fr" "Me" "Fr" "Ga" "Ge" "Ge" "Gh" "Gr" "Gr" "Gu" "Ho" "Ho" "Hu" "Ic" [31] "In" "In" "Ir" "Ir" "Ir" "Is" "It" "Ja" "Ja" "Jo" "Ka" "Ke" "Mo" "Na" "Ne" [46] "Ne" "Ni" "No" "Om" "Pa" "Pe" "Ph"