从字符串中提取十进制数 [英] Extracting decimal numbers from a string

问题描述

我有一个字符串，例如 "3.1 ml" 或 "abc 3.1 xywazw"

I have a string such as "3.1 ml" or "abc 3.1 xywazw"

我想从这个字符串中提取"3.1".我在 stackoverflow 上发现了很多关于从字符串中提取数字的问题，但没有解决方案适用于十进制数字的情况.

I'd like to extract "3.1" from this string. I have found many questions on stackoverflow about the extraction of numbers from a character string, but no solution works for the case of decimal numbers.

推荐答案

此方法使小数点和小数部分可选，并允许提取多个数字:

This approach makes the decimal point and decimal fraction optional and allows multiple numbers to be extracted:

str <- " test 3.1 test 5"
as.numeric(unlist(regmatches(str,
                             gregexpr("[[:digit:]]+\\.*[[:digit:]]*",str))
          )      )
#[1] 3.1 5.0

关于负数的问题可以通过可选的 perl 样式前瞻来解决:

The concern about negative numbers can be address with optional perl style look-ahead:

 str <- " test -4.5 3.1 test 5"
    as.numeric(unlist(regmatches(str,gregexpr("(?>-)*[[:digit:]]+\\.*[[:digit:]]*",str, perl=TRUE))))

#[1] -4.5  3.1  5.0

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