修剪数据框中字符串的一部分

Question

如果我有这样的数据帧结构：

AA1_123.zip
BB2_456.txt
CCC_789.doc

如何将其更改为：

AA1
BB2
CCC

Answer 1

您可以尝试sub

sub('_.*', '', df1$Col)
#[1] "AA1" "BB2" "CCC"

数据

df1 <- structure(list(Col = c("AA1_123.zip", "BB2_456.txt", 
"CCC_789.doc"
)), .Names = "Col", class = "data.frame", row.names = c(NA, -3L))

Answer 2

如果字符串在开头都是相同的样式，下划线前有三个字符，这将起作用：

df1 <- structure(list(Col = c("AA1_123.zip", "BB2_456.txt", 
                              "CCC_789.doc"
)), .Names = "Col", class = "data.frame", row.names = c(NA, -3L))

> substr(df1$Col, 1, 3)
[1] "AA1" "BB2" "CCC"

Answer 3

您还可以再次阅读该列，使用comment.char = "_"清除该行的其余部分。 ÿ

df <- data.frame(x = c("AA1_123.zip", "BB2_456.txt", "CCC_789.doc"))

read.table(text = as.character(df$x), comment.char="_")
#    V1
# 1 AA1
# 2 BB2
# 3 CCC

或者您可以使用scan()

scan(text = as.character(df$x), what = "", comment.char="_")
# Read 3 items
# [1] "AA1" "BB2" "CCC"