extract numeric value from number, NA and character string - r

Question

I have a column mixture with number, text, NA values. I just want to extract numeric value from col2
col1 <- c('t1', 't2', 't3', 't4', 't5', 't6', 't7', 't8', 't9', 't10')
col2 <- c(300, '>200m', NA, 'result 50 mg/g', NA, 'Not data', 'pending', NA, 'positive', 'data >20 mile/h')
df <- data.frame(col1, col2)
My intention is:
All numbers will remain numeric
NA values will remain NA
Character/text will be converted to NA value
Extract number if it's mixture with text (e.g., 'data >20 mile/h' to 20)
The expected output (col3) will be like this:
col3 <- c(300, 200, NA, 50, NA, NA, NA, NA, NA, 20)
df2 <- data.frame(col1, col3)

Answer 1

Using str_extract from stringr to extract the numbers.
library(stringr)
cbind(df, col3 = as.numeric(str_extract(df$col2, "[\\d+.]+")))
col1 col2 col3
1 t1 300 300.0
2 t2 >200m 200.0
3 t3 wef3.2 wef 3.2
4 t4 result 50 mg/g 50.0
5 t5 <NA> NA
6 t6 Not data NA
7 t7 pending NA
8 t8 <NA> NA
9 t9 positive NA
10 t10 data >20 mile/h 20.0
Using gsub, removing everything but numbers.
cbind(df, col3 = as.numeric(
gsub("([.-])|[[:alpha:][:punct:] ]", "\\1", df$col2)))
col1 col2 col3
1 t1 300 300.0
2 t2 >200m 200.0
3 t3 wef3.2 wef 3.2
4 t4 result 50 mg/g 50.0
5 t5 <NA> NA
6 t6 Not data NA
7 t7 pending NA
8 t8 <NA> NA
9 t9 positive NA
10 t10 data >20 mile/h 20.0
Or use \\D (non-digits) instead [:alpha:] and [:punct:] (Thx to #thelatemail and #onyambu)!
Data
df <- structure(list(col1 = c("t1", "t2", "t3", "t4", "t5", "t6", "t7",
"t8", "t9", "t10"), col2 = c("300", ">200m", "wef3.2 wef", "result 50 mg/g",
NA, "Not data", "pending", NA, "positive", "data >20 mile/h")),
row.names = c(NA, -10L), class = "data.frame")

Answer 2

One potential option is to use parse_number() from the readr package, e.g.
library(readr)
col1 <- c('t1', 't2', 't3', 't4', 't5', 't6', 't7', 't8', 't9', 't10')
col2 <- c(300, '>200m', NA, 'result 50 mg/g', NA, 'Not data', 'pending', NA, 'positive', 'data >20 mile/h')
df <- data.frame(col1, col2)
df$col3 <- parse_number(df$col2)
#> Warning: 3 parsing failures.
#> row col expected actual
#> 6 -- a number Not data
#> 7 -- a number pending
#> 9 -- a number positive
df
#> col1 col2 col3
#> 1 t1 300 300
#> 2 t2 >200m 200
#> 3 t3 <NA> NA
#> 4 t4 result 50 mg/g 50
#> 5 t5 <NA> NA
#> 6 t6 Not data NA
#> 7 t7 pending NA
#> 8 t8 <NA> NA
#> 9 t9 positive NA
#> 10 t10 data >20 mile/h 20
Created on 2023-02-07 with reprex v2.0.2