Say I have a string such as "J1P3V9". I also have strings such as "0H44J4". I want to only detect string which follow the first patter of Letter, Number, Letter, Number, Letter, Number.
What is a regex expression to match only these instances?
This regex does your job,
\b([A-Z]\d){3}\b
\b makes sure it doesn't match partially in a bigger string.
Demo
In case you want to include lowercase alphabets too, the regex becomes,
\b([a-zA-Z]\d){3}\b
Try the following regex.
s <- c("J1P3V9", "0H44J4")
pattern <- paste(rep("[[:alpha:]][[:digit:]]", 3), collapse = "")
grep(pattern, s, value = TRUE)
#[1] "J1P3V9"
You might use
\b(?:[a-zA-Z]\d){3}\b
See a demo on regex101.com.
Or, more verbose but not supported in R:
(?(DEFINE)
(?<letter>[a-zA-Z])
(?<number>\d)
)
\b(?:(?&letter)(?&number)){3}\b
Jokes aside, don't rely on \w which is a shortcut for [a-zA-z0-9_] and will most likely match more than you want.
You can use this regex:
(?:[A-Z]\\d){3}
Usage:
mystring <- c("J1P3V9", "0H44J4")
grepl("(?:[A-Z]\\d){3}", mystring)
# [1] TRUE FALSE
Related
I have the string in R
BLCU142-09|Apodemia_mejicanus
and I would like to get the result
Apodemia_mejicanus
Using the stringr R package, I have tried
str_replace_all("BLCU142-09|Apodemia_mejicanus", "[[A-Z0-9|-]]", "")
# [1] "podemia_mejicanus"
which is almost what I need, except that the A is missing.
You can use
sub(".*\\|", "", x)
This will remove all text up to and including the last pipe char. See the regex demo. Details:
.* - any zero or more chars as many as possible
\| - a | char (| is a special regex metacharacter that is an alternation operator, so it must be escaped, and since string literals in R can contain string escape sequences, the | is escaped with a double backslash).
See the R demo online:
x <- c("BLCU142-09|Apodemia_mejicanus", "a|b|c|BLCU142-09|Apodemia_mejicanus")
sub(".*\\|", "", x)
## => [1] "Apodemia_mejicanus" "Apodemia_mejicanus"
We can match one or more characters that are not a | ([^|]+) from the start (^) of the string followed by | in str_remove to remove that substring
library(stringr)
str_remove(str1, "^[^|]+\\|")
#[1] "Apodemia_mejicanus"
If we use [A-Z] also to match it will match the upper case letter and replace with blank ("") as in the OP's str_replace_all
data
str1 <- "BLCU142-09|Apodemia_mejicanus"
You can always choose to _extract rather than _remove:
s <- "BLCU142-09|Apodemia_mejicanus"
stringr::str_extract(s,"[[:alpha:]_]+$")
## [1] "Apodemia_mejicanus"
Depending on how permissive you want to be, you could also use [[:alpha:]]+_[[:alpha:]]+ as your target.
I would keep it simple:
substring(my_string, regexpr("|", my_string, fixed = TRUE) + 1L)
I have a string like word_string. What I want is Word_String. If I use the function str_to_title from stringr, what I get is Word_string. It does not capitalize the second word.
Does anyone know any elegant way to achieve that with stringr? Thanks!
Here is a base R option using sub:
input <- "word_string"
output <- gsub("(?<=^|_)([a-z])", "\\U\\1", input, perl=TRUE)
output
[1] "Word_String"
The regex pattern used matches and captures any lowercase letter [a-z] which is preceded by either the start of the string (i.e. it's the first letter) or an underscore. Then, we replace with the uppercase version of that single letter. Note that the \U modifier to change to uppercase is a Perl extension, so we must use sub in Perl mode.
Can also use to_any_case from snakecase
library(snakecase)
to_any_case(str1, "title", sep_out = "_")
#[1] "Word_String"
data
str1 <- "word_string"
This is obviously overly complicating but another base possibility:
test <- "word_string"
paste0(unlist(lapply(strsplit(test, "_"),function(x)
paste0(toupper(substring(x,1,1)),
substring(x,2,nchar(x))))),collapse="_")
[1] "Word_String"
You could first use gsub to replace "_" by " " and apply the str_to_title function
Then use gsub again to change it back to your format
x <- str_to_title(gsub("_"," ","word_string"))
gsub(" ","_",x)
I am new to REGEX. As per title, I would like to capture abc-def-ghi in the string utm_campaign=abc-def-ghi. The string is usually embedded in an url. Using the following pattern (utm_campaign=[a-zA-Z0-9_-]+) I can match the entire string, but I really just want the second part of the string, which is abc-def-ghi. Is there an efficient way to do this in regex? Preferable language for this question is R.
Another option: gsub
> string <- "utm_campaign=abc-def-ghi"
> gsub(".*=(\\w*)", "\\1", string)
[1] "abc-def-ghi"
See regex in use here
(?<=utm_campaign=)[\w-]+
(?<=utm_campaign=) Positive lookbehind ensuring what precedes matches utm_campaign= literally
[\w-]+ Match any word character (a-zA-Z0-9_) or hyphen character one or more times
See code in use here
x <- "utm_campaign=abc-def-ghi"
m <- regexpr("(?<=utm_campaign=)[\\w-]+", x, perl=TRUE)
regmatches(x, m)
Result: abc-def-ghi
Here are some examples from my data:
a <-c("sp|Q9Y6W5|","sp|Q9HB90|,sp|Q9NQL2|","orf|NCBIAAYI_c_1_1023|",
"orf|NCBIACEN_c_10_906|,orf|NCBIACEO_c_5_1142|",
"orf|NCBIAAYI_c_258|,orf|aot172_c_6_302|,orf|aot180_c_2_405|")
For a: The individual strings can contain even more entries of "sp|" and "orf"
The results have to be like this:
[1] "sp|Q9Y6W5" "sp|Q9HB90,sp|Q9NQL2" "orf|NCBIAAYI_c_1_1023"
"orf|NCBIACEN_c_10_906,orf|NCBIACEO_c_5_1142"
"orf|NCBIAAYI_c_258,orf|aot172_c_6_302,orf|aot180_c_2_405"
So the aim is to remove the last "|" for each "sp|" and "orf|" entry. It seems that "|" is a special challenge because it is a metacharacter in regular expressions. Furthermore, the length and composition of the "orf|" entries varying a lot. The only things they have in common is "orf|" or "sp|" at the beginning and that "|" is on the last position. I tried different things with gsub() but also with the stringr package or regexpr() or [:punct:], but nothing really worked. Maybe it was just the wrong combination.
We can use gsub to match the | that is followed by a , or is at the end ($) of the string and replace with blank ("")
gsub("[|](?=(,|$))", "", a, perl = TRUE)
#[1] "sp|Q9Y6W5"
#[2] "sp|Q9HB90,sp|Q9NQL2"
#[3] "orf|NCBIAAYI_c_1_1023"
#[4] "orf|NCBIACEN_c_10_906,orf|NCBIACEO_c_5_1142"
#[5] "orf|NCBIAAYI_c_258,orf|aot172_c_6_302,orf|aot180_c_2_405"
Or we split by ,', remove the last character withsubstr, andpastethelist` elements together
sapply(strsplit(a, ","), function(x) paste(substr(x, 1, nchar(x)-1), collapse=","))
An easy alternative that might work. You need to escape the "|" using "\\|".
# Input
a <-c("sp|Q9Y6W5|","sp|Q9HB90|,sp|Q9NQL2|","orf|NCBIAAYI_c_1_1023|",
"orf|NCBIACEN_c_10_906|,orf|NCBIACEO_c_5_1142|",
"orf|NCBIAAYI_c_258|,orf|aot172_c_6_302|,orf|aot180_c_2_405|")
# Expected output
b <- c("sp|Q9Y6W5", "sp|Q9HB90,sp|Q9NQL2", "orf|NCBIAAYI_c_1_1023" ,
"orf|NCBIACEN_c_10_906,orf|NCBIACEO_c_5_1142" ,
"orf|NCBIAAYI_c_258,orf|aot172_c_6_302,orf|aot180_c_2_405")
res <- gsub("\\|,", ",", gsub("\\|$", "", a))
all(res == b)
#[1] TRUE
You could construct a single regex call to gsub, but this is simple and easy to understand. The inner gsub looks for | and the end of the string and removes it. The outer gsub looks for ,| and replaces with ,.
You do not have to use a PCRE regex here as all you need can be done with the default TRE regex (if you specify perl=TRUE, the pattern is compiled with a PCRE regex engine and is sometimes slower than TRE default regex engine).
Here is the single simple gsub call:
gsub("\\|(,|$)", "\\1", a)
See the online R demo. No lookarounds are really necessary, as you see.
Pattern details
\\| - a literal | symbol (because if you do not escape it or put into a bracket expression it will denote an alternation operator, see the line below)
(,|$) - a capturing group (referenced to with \1 from the replacement pattern) matching either of the two alternatives:
, - a comma
| - or (the alternation operator)
$ - end of string anchor.
The \1 in the replacement string tells the regex engine to insert the contents stored in the capturing group #1 back into the resulting string (so, the commas are restored that way where necessary).
I have two related questions regarding regular expressions in R:
[1]
I would like to convert sub-strings, containing punctuation followed by a letter, to an upper case letter.
Example:
Dr_dre to: DrDre
Captain.Spock to: CaptainSpock
spider-man to: spiderMan
[2]
I would like convert camel case strings to lower case strings with underscore delimiter.
Example:
EndOfFile to: End_of_file
CamelCase to: Camel_Case
ABC to: A_B_C
Thanks much,
Kamashay
We can use sub. We match one or more punctuation characters ([[:punct:]]+) followed by a single character which is captured as a group ((.)). In the replacement, the backreference for the capture group (\\1) is changed to upper case (\\U).
sub("[[:punct:]]+(.)", "\\U\\1", str1, perl = TRUE)
#[1] "DrDre" "CaptainSpock" "spiderMan"
For the second case, we use regex lookarounds i.e. match a letter ((?<=[A-Za-z])) followed by a capital letter and replace with _.
gsub("(?<=[A-Za-z])(?=[A-Z])", "_", str2, perl = TRUE)
#[1] "End_Of_File" "Camel_Case" "A_B_C"
data
str1 <- c("Dr_dre", "Captain.Spock", "spider-man")
str2 <- c("EndOfFile", "CamelCase", "ABC")