Re: Question about DeleteCases to remove list elements based on first character

*To*: mathgroup at smc.vnet.net*Subject*: [mg124323] Re: Question about DeleteCases to remove list elements based on first character*From*: "Scot T. Martin" <smartin at seas.harvard.edu>*Date*: Tue, 17 Jan 2012 03:21:00 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

Andrew, there are several ways to get this result, and you were almost there. Here's one example below. The key point is to recognize that you have a list (i.e., not a String action) for which you wish to do a test (i.e., by String actions) on the list elements. In[1]:= ?Pick Pick[list,sel] picks out those elements of list for which the corresponding element of sel is True. In[2]:= ?StringMatchQ StringMatchQ["string",patt] tests whether "string" matches the string pattern patt. In[3]:= list = {"abc", ";def", "ghi", ";jkl", "; mno", "pqr;X"} Out[3]= {"abc", ";def", "ghi", ";jkl", "; mno", "pqr;X"} In[4]:= sel = Not[StringMatchQ[#, ";" ~~ __]] & /@ list Out[4]= {True, False, True, False, False, True} In[5]:= Pick[list, sel] Out[5]= {"abc", "ghi", "pqr;X"} ________________________________________ From: Andrew DeYoung [adeyoung at andrew.cmu.edu] Sent: Monday, January 16, 2012 17:06 To: mathgroup at smc.vnet.net Subject: [mg124323] Question about DeleteCases to remove list elements based on first character Hi, I have a list of strings in which some elements begin with the ";" character and some do not. The ";" character indicates a program comment, so I wish to drop all elements in the list that begin with the ";" character. As a simplified example, suppose I have the following list S: S = {"abc", ";def", "ghi", ";jkl", "; mno", "pqr;X"} I wish to drop from S all elements that begin with ";". So, I want to obtain: {"abc", "ghi", "pqr;X"} Will you please help me know how to do this? Can this be done with DeleteCases? For example, I tried: DeleteCases[S, StringTake[#, 1] == ";"&] and DeleteCases[S, ";" ~~ __] but I am wrong: these do not work. Can you please help me? Thanks so much. Andrew DeYoung Carnegie Mellon University