[英]Extracting decimal numbers from a string
I have a string such as "3.1 ml"
or "abc 3.1 xywazw"
我有一个字符串,如
"3.1 ml"
或"abc 3.1 xywazw"
I'd like to extract "3.1"
from this string. 我想从这个字符串中提取
"3.1"
。 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. 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。
Use the stringr
library: 使用
stringr
库:
x<-"abc 3.1 xywazw"
str_extract(x, "\\d+\\.*\\d*")
[1] "3.1"
This approach makes the decimal point and decimal fraction optional and allows multiple numbers to be extracted: 此方法使小数点和小数部分可选,并允许提取多个数字:
str <- " test 3.1 test 5"
as.numeric(unlist(regmatches(str,
gregexpr("[[:digit:]]+\\.*[[:digit:]]*",str))
) )
#[1] 3.1 5.0
The concern about negative numbers can be address with optional perl style look-ahead: 关于负数的担忧可以通过可选的perl样式预测来解决:
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
Regular expression for floating point number from http://www.regular-expressions.info/floatingpoint.html with minor adjustment to work in R. 来自http://www.regular-expressions.info/floatingpoint.html的浮点数的正则表达式,并在R中进行微调。
s <- "1e-6 dkel"
regmatches(s,gregexpr("[-+]?[0-9]*\\.?[0-9]+([eE][-+]?[0-9]+)?",s))
> [[1]]
> [1] "1e-6"
You can use regular expressions : 您可以使用正则表达式:
> str <- " test 3.1 test"
> as.numeric(regmatches(str,regexpr("[[:digit:]]+\\.[[:digit:]]+",str)))
[1] 3.1
regexpr
returns the start position and length of the matched string. regexpr
返回匹配字符串的起始位置和长度。 regmatches
returns the matches. regmatches
返回匹配。 You can then convert it to a number. 然后,您可以将其转换为数字。
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