R：如何将数据帧值缩短为第一个字符

Question

I would like to shorten the values of one column of my data.frame. Right now, each value consists of many letters, such as

df$col1
[1] AHG    ALK    OPH   BCZ   LKH    QRQ    AAA   VYY

what I need is only the first letter:

df$col1
[1] A    A    O   B   L    Q    A   V

I have read other entries that suggested to use gsub , stri_replace_all_charclass , or strsplit . But I am afraid I need help to implement this.

Answer 1

你可以使用strtrim

df$col1 <- strtrim(df$col1, 1)

Answer 2

The stringr package is great:

require(stringr)

df <- data.frame(col1 = c("AHG", "ALK", "OPH", "BCZ", "LKH", "QRQ", "AAA", "VYY"))

str_sub(df$col1, 1, 1)

[1] "A" "A" "O" "B" "L" "Q" "A" "V"

Answer 3

你需要的是子串函数：

df$col1 <- substr(df$col1, 1, 1)

Answer 4

I agree with Robin. using the substr or substring function will directly do the trick without having to install any package.

df$col1 <- substr(df$col1, 1, 1)

or df$col1 <- substring(df$col1,1,1)

use syntax substr (target vector, start place, stop place)