Using grep to help subset a data frame in R

Question

I am having trouble subsetting my data   I want the data subsetted on column x  where the first 3 characters begin G45   My data frame    x  lt - c  G448    G459    G479    G406      y  lt - c 1 4   My Data  lt - data frame  x y    I have tried    subset  My Data  x   G45      But I am unsure how to use wildcards   I have also tried grep   to find the indicies    grep    G45    My Data x    but it returns all 4 rows  rather than just those beginning G45  probably also as I am unsure how to use wildcards

User · Answer

You may also use the stringr package  library dplyr  library stringr  My Data   gt   filter str detect x    G45      You may not use      starts with  in this case  to obtain the results you need

User · Answer

It s pretty straightforward using   to extract   grep will give you the position in which it matched your search pattern  unless you use value   TRUE     grep   G45   My Data x     1  2   Since you re searching within the values of a single column  that actually corresponds to the row index  So  use that with    where you would use My Data rows  cols  to get specific rows and columns    My Data grep   G45   My Data x            x y   2 G459 2     The help-page for subset shows how you can use grep and grepl with subset if you prefer using this function over    Here s an example   subset My Data  grepl   G45   My Data x          x y   2 G459 2     As of R 3 3  there s now also the startsWith function  which you can again use with subset  or with any of the other approaches above   According to the help page for the function  it s considerably faster than using substring or grepl   subset My Data  startsWith as character x    G45           x y   2 G459 2

[r] Using grep to help subset a data frame in R

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