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I have character strings with two underscores. Like these
c54254_g4545_i5454
c434_g4_i455
c5454_g544_i3
.
.
etc
I need to split these strings by the second underscore and I am afraid I have no clue how to do that in R (or any other tool for that sake). I'd be very happy if anyone can sort me out here. Thank you SM
966
To split a string in R, use the strsplit() method. The strsplit() is a built-in R function that splits the string vector into sub-strings. The strsplit() method returns the list, where each list item resembles the item of input that has been split.
To split a string with specific character as delimiter in Java, call split() method on the string object, and pass the specific character as argument to the split() method. The method returns a String Array with the splits as elements in the array.
Note that splitting into single characters can be done via split = character(0) or split = "" ; the two are equivalent.
To split a string by underscore in Python, pass the underscore character "_" as a delimiter to the split() function. It returns a list of strings resulting from splitting the original string on the occurrences of "_" .
One way would be to replace the second underscore by another delimiter (i.e. space) using sub and then split using that.
Using sub, we match one or more characters that are not a _ from the beginning (^) of the string (^[^_]+) followed by the first underscore (_) followed by one or characters that are not a _ ([^_]+). We capture that as a group by placing it inside the parentheses ((....)), then we match the _ followed by one or more characters till the end of the string in the second capture group ((.*)$). In the replacement, we separate the first (\\1) and second (\\2) with a space.
strsplit(sub('(^[^_]+_[^_]+)_(.*)$', '\\1 \\2', v1), ' ')
#[[1]]
#[1] "c54254_g4545" "i5454"
#[[2]]
#[1] "c434_g4" "i455"
#[[3]]
#[1] "c5454_g544" "i3"
v1 <- c('c54254_g4545_i5454', 'c434_g4_i455', 'c5454_g544_i3')
strsplit(sub("(_)(?=[^_]+$)", " ", x, perl=T), " ")
#[[1]]
#[1] "c54254_g4545" "i5454"
#
#[[2]]
#[1] "c434_g4" "i455"
#
#[[3]]
#[1] "c5454_g544" "i3"
With the pattern "(_)(?=[^_]+$)", we split on an underscore that comes before a series of one or more non-underscore characters. That way we only need one capture group.
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