regex

• http://regexr.com: Test out your reg expressions before you use them (specify your test expression and it will highlight in a sample document (which you can change) the matches.
• regex base-R cheat sheet
• Helpful examples on grouping
• Examples on subsetting matches
• Getting strsplit in the right format with sapply
• RegexBuddy

Drew’s example (using gsub):

Searching through these ugly column headings in data frame called x:

Raw Data (595) 1 - 0 h  
Raw Data (595) 5 - 0 h 30 min 
Raw Data (595) 7 - 1 h  
Raw Data (595) 10 - 1 h 30 min 
Raw Data (595) 13 - 2 h  
Raw Data (595) 16 - 2 h 30 min 

x <- read.delim("x.txt",header=F,stringsAsFactors = FALSE)

I used the following gsub() statement (within an apply() function, but that’s not important here) on data frame x:

gsub('\\.*(\\d*) h (\\d*).*', '\\1.0\\2',x[[1]])

## [1] "Raw Data (595) 1 - 0.0"    "Raw Data (595) 5 - 0.030" 
## [3] "Raw Data (595) 7 - 1.0"    "Raw Data (595) 10 - 1.030"
## [5] "Raw Data (595) 13 - 2.0"   "Raw Data (595) 16 - 2.030"

(On a second look, it’s possible the initial \\.* isn’t necessary, but as always, test your regex’s out before executing them)

perl example

gsub('\\.*(\\d*)\\sh\\s(\\d*).*', '\\1.0\\2',x[[1]], perl=T)

## [1] "Raw Data (595) 1 - 0.0"    "Raw Data (595) 5 - 0.030" 
## [3] "Raw Data (595) 7 - 1.0"    "Raw Data (595) 10 - 1.030"
## [5] "Raw Data (595) 13 - 2.0"   "Raw Data (595) 16 - 2.030"

\\s means “space” which would also match \\t and \\n
\\d{2} means 2 digits
[5-9] [a-z] \W \D

And it catches the following substrings (highlighted in cyan):

Raw Data (595) 1 - 0 h  
Raw Data (595) 5 - 0 h 30 min 
Raw Data (595) 7 - 1 h  
Raw Data (595) 10 - 1 h 30 min 
Raw Data (595) 13 - 2 h  
Raw Data (595) 16 - 2 h 30 min 

d <- data.frame(c("Raw Data (595) 1 - 0 h",  
  "Raw Data (595) 5 - 0 h 30 min",
  "Raw Data (595) 7 - 1 h",
  "Raw Data (595) 10 - 1 h 30 min",
  "Raw Data (595) 13 - 2 h",
  "Raw Data (595) 16 - 2 h 30 min" ))
class(d)

## [1] "data.frame"

dim(d)

## [1] 6 1

dl <- as.list(d)

[1] 6 1
[1] "data.frame"

Perl =T version

gsub('\\.*(\\d*)\\sh\\s(\\d*).*', '\\1.0\\2',d, perl=T)

## [1] "c(1, 5, 6, 2, 3, 4)"

gsub('\\.*(\\d*)\\sh\\s(\\d*).*', '\\1.0\\2',dl, perl=T)

## [1] "c(1, 5, 6, 2, 3, 4)"

[1] "c(1, 5, 6, 2, 3, 4)"
[1] "c(1, 5, 6, 2, 3, 4)"

Non Perl version:

gsub('\\.*(\\d*) h (\\d*).*', '\\1.0\\2',d)

## [1] "c(1, 5, 6, 2, 3, 4)"

gsub('\\.*(\\d*) h (\\d*).*', '\\1.0\\2',dl)

## [1] "c(1, 5, 6, 2, 3, 4)"

[1] "c(1, 5, 6, 2, 3, 4)"
[1] "c(1, 5, 6, 2, 3, 4)"

Drew Doering used this in the context of converting time values in the format “X h Y min” to a decimal hour format, to facilitate downstream analysis/plotting. You can see that specific command in-context here on line 49: https://github.com/dtdoering/grofitr/blob/b70f82755e83ad27b4ebe07c9e78b3cc36159351/findRates.R

However, playing with this in my own instance of RStudio, it doesn’t seem to be doing what I wanted it to do with that specific command. Here is a reproducible example you can use to replace that last command at the bottom:

timePoints <- c("Raw Data (595) 1 - 0 h",
                "Raw Data (595) 5 - 0 h 30 min",
                "Raw Data (595) 7 - 1 h", 
                "Raw Data (595) 10 - 1 h 30 min", 
                "Raw Data (595) 13 - 2 h", 
                "Raw Data (595) 16 - 2 h 30 min",
                "Raw Data (595) 50 - 21 h 30 min")

sapply(timePoints,
       function(x) gsub('.* - (\\d*) h( (\\d*).*)?', 
                        '\\1.0\\3',
                        x, perl = F), 
       USE.NAMES = FALSE)

## [1] "0.0"    "0.030"  "1.0"    "1.030"  "2.0"    "2.030"  "21.030"

Drew would then go on to do some string operations and arithmetic to divide the right side of the decimal by 60.