根据 R 中前面的特定单词和后面的 % 符号提取字符串或值

Question

I have a Text column with thousands of rows of paragraphs, and I want to extract the values of " Capacity > x% ". The operation sign can be >,<,=, ~... I basically need the operation sign and integer value (eg <40%) and place it in a column next to the it, same row. I have tried, removing before/after text, gsub, grep , grepl, string_extract , etc. None with good results. I am not sure if the percentage sign is throwing it or I am just not getting the code structure. Appreciate your assistance please. Here are some codes I have tried (aa is the df, TEXT is col name):

str_extract(string =aa$TEXT, pattern = perl("(?<=LVEF).*(?=%)"))

gsub(".*[Capacity]([^.]+)[%].*", "\\1", aa$TEXT)

genXtract(aa$TEXT, "Capacity", "%")

gsub("%.*$", "%", aa$TEXT)

grep("^Capacity.*%$",aa$TEXT)

Answer 1

Since you did not provide a reproducible example, I created one myself and used it here.

We can use sub to extract everything after "Capacity" until a number and % sign.

sub(".*Capacity(.*\\d+%).*", "\\1", aa$TEXT)
#[1] " > 10%"  " < 40%"  " ~ 230%"

Or with str_extract

stringr::str_extract(aa$TEXT, "(?<=Capacity).*\\d+%")

data

aa <- data.frame(TEXT = c("This is a temp text, Capacity > 10%", 
                    "This is a temp text, Capacity < 40%", 
                    "Capacity ~ 230% more text  ahead"), stringsAsFactors = FALSE)

Answer 2

gsub solution

I think your gsub solution was pretty close, but didn't bring along the percentage sign as it's outside the brackets. So something like this should work (the result is assigned to the capacity column):

aa$capacity <- gsub(".*[Capacity]([^.]+%).*", "\\\\1", aa$TEXT)

Alternative method

The gsub approach will match the whole string when there is no operator match. To avoid this, we can use the stringr package with a more specific regular expression:

library(magrittr)
library(dplyr)
library(stringr)

aa %>% 
  mutate(capacity = str_extract(TEXT, "(?<=Capacity\\s)\\W\\s?\\d+\\s?%")) %>%
  mutate(Capacity = str_squish(Capacity)) # Remove excess white space

This code will give NA when there is no match, which I believe is your desired behaviour.