Currently as the first column in a data frame I have string values in the
format xx_yy - I want to create a new column with just the substring xx (for
each row in turn). Three possible ways to do this might be (1) split the
string by '_' using strsplit and paste the first of the resulting variables
into a new column, but I have been unable to do this for each row of my data
frame in turn (trying to use apply); (2) split the column into two based on
'_', but I am not sure if this is possible; (3) use a regular expression to
return the substring up to the '_', but I am unsure how to make a regular
expression return the substring it matches to in R.
Any ideas on all three counts would be gratefully recieved.
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