从 R 中的字符串中提取数字和文本

Question

I have a string and would like to extract the first sets of three numbers and any three letters next to each number and then put into a vector. So this:

t1 <- "The string contains numbers ranging from 3-4 cm and can reach up to 5.6 m long, and sometimes can even reach 10 m."

t1 would become:

"3-4 cm", "5.6 m", "10m"

I have looked up various regular expression functions like grep, grepl etc., but can't find example that matches my query. Any suggestions?

Answer 1

Here's how this can be done with gregexpr() + regmatches() :

ipartRE <- '\\d+';
fpartRE <- '\\.\\d+';
numRE <- paste0(ipartRE,'(?:',fpartRE,')?');
rangeRE <- paste0(numRE,'(?:\\s*-\\s*',numRE,')?');
pat <- paste0(rangeRE,'\\s*[a-zA-Z]{1,3}\\b');
regmatches(t1,gregexpr(perl=T,pat,t1))[[1L]];
## [1] "3-4 cm" "5.6 m"  "10 m"

I built up the regex incrementally from component parts for human readability, but obviously you don't need to do that.

---

To match the new pattern we need to accept an alternation for the second number which takes matching parentheses around the number. I also found that the dash in 120(–150) cm in not a normal ASCII hyphen , but is an en dash , and so I added another precomputed regular expression piece called dashRE which matches all 3 common dash types (ASCII, en dash, and em dash ):

ipartRE <- '\\d+';
fpartRE <- '\\.\\d+';
numRE <- paste0(ipartRE,'(?:',fpartRE,')?');
dashRE <- '[—–-]';
rangeOptParenRE <- paste0(numRE,'(?:\\s*(?:',dashRE,'\\s*',numRE,'|\\(\\s*',dashRE,'\\s*',numRE,'\\s*\\)\\s*))?');
pat <- paste0(rangeOptParenRE,'\\s*[a-zA-Z]{1,3}\\b');
regmatches(t1,gregexpr(perl=T,pat,t1))[[1L]];
## [1] "3-4 cm"       "120(–150) cm" "5.6 m"        "10 m"

Answer 2

You can try this regular expression [0-9.-]+\\\\s+[a-zA-z]{1,3} and use the str_extract_all from stringr package to extract them:

stringr::str_extract_all(t1, "[0-9.-]+\\s+[a-zA-Z]{1,3}")
[[1]]
[1] "3-4 cm" "5.6 m"  "10 m"