Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2012

[Date Index] [Thread Index] [Author Index]

Search the Archive

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



  • Prev by Date: Re: Nested Manipulate copies to clipboard as "grey box"
  • Next by Date: Re: opposite of AppendTo
  • Previous by thread: Re: Question about DeleteCases to remove list elements based on first character
  • Next by thread: Re: Question about DeleteCases to remove list elements based on first character