Re: Re: Re: Using Select with arrays? (Relative newbie)

*To*: mathgroup at smc.vnet.net*Subject*: [mg54294] Re: [mg54244] Re: Re: Using Select with arrays? (Relative newbie)*From*: DrBob <drbob at bigfoot.com>*Date*: Wed, 16 Feb 2005 14:36:16 -0500 (EST)*References*: <cup5ip$dsr$1@smc.vnet.net> <200502140557.AAA17011@smc.vnet.net> <200502150250.VAA27254@smc.vnet.net>*Reply-to*: drbob at bigfoot.com*Sender*: owner-wri-mathgroup at wolfram.com

This is much simpler, I think: data = { {1, 1, "string1", c, d}, {1, 2, "string2", c, d}, {1, 3, "string3", c, d}, {1, 4, "string4", c, d}, {2, 1, "string1", c, d}, {2, 2, "string2", c, d}, {3, 1, "string3", c, d}, {4, 1, "string2", c, d}, {4, 2, "string4", c, d}}; Cases[data, {1, Max[data[[All, 2]]], _String, _, _}] {{1, 4, string4, c, d}} Bobby On Mon, 14 Feb 2005 21:50:36 -0500 (EST), Hugo Mallinson <hfm21 at cam.ac.uk> wrote: > Thanks very much! My typos didn't help matters (the strings were > actually strings, I just left out the quotes to simplify things..or so > I thought). This appears to be more efficient than what I eventually > came up with: > Select[data, #[[1]]==1 && #[[4]]=="string"] and then a separate Max[] > call. > > Hugo > > On Feb 14, 2005, at 5:57 AM, Curt Fischer wrote: > >> Hugo Mallinson wrote: >>> The subject might not be entirely correct, but here is my problem: >>> >>> I have a list of 5-variable data points like >>> >>> data = { >>> {1, 1, string1, c, d} >>> {1, 2, string2, c, d} >>> {1, 3, string3, c, d} >>> {1, 4, string4, c, d} >>> {2, 1, string1, c, d} >>> {2, 2, string2, c, d} >>> {3, 1, string3, c, d} >>> {4, 1, string2, c, d} >>> {4, 2, string4, c, d} >>> } >>> >>> >>> and I want to extract just the points that have 1 (or 2, etc) as their >>> first value. I think I should do something like >>> >>> Select[data, {1, _Integer, _String, _Integer, _Integer}] >>> >>> but that doesn't work. >> >> None of your data matches the pattern you made. When you enter things >> like string2 or c or d into Mathematica without quotation marks, they >> are not strings or integers. You can easily find out what Mathematica >> thinks they are. >> >> In[1]:= >> data = {{1, 1, >> string1, c, d} , {1, 2, string2, c, d}, {1, 3, >> string3, c, d}, {1, 4, string4, c, d} , {2, 1, >> string1, c, d}, {2, 2, string2, c, d}, {3, 1, >> string3, c, d} , {4, 1, string2, c, d}, {4, 2, string4, c, d}}; >> >> In[2]:= >> Map[Head, data, {2}] >> Out[2]= >> {{Integer, Integer, Symbol, Symbol, Symbol}, {Integer, Integer, Symbol, >> Symbol, Symbol}, { >> Integer, Integer, Symbol, Symbol, Symbol}, {Integer, Integer, >> Symbol, >> Symbol, Symbol}, { >> Integer, Integer, Symbol, Symbol, Symbol}, {Integer, Integer, >> Symbol, >> Symbol, Symbol}, { >> Integer, Integer, Symbol, Symbol, Symbol}, {Integer, Integer, >> Symbol, >> Symbol, Symbol}, {Integer, Integer, Symbol, Symbol, Symbol}} >> >> That is, they are all Symbols. We can re-write your pattern to be more >> flexible and we can use Cases[] instead of Select[]. (IME Cases[] is >> easier to figure out.) >> >> In[3]:= >> Cases[data, {1, _Integer, _, _, _}] >> Out[3]= >> {{1, 1, string1, c, d}, {1, 2, string2, c, d}, { >> 1, 3, string3, c, d}, {1, 4, string4, c, d}} >> >> So that gets you the preliminary result. But you want to extract the >> member of this list that has the maximal second element. >> >>> Having done that I need to find the maximum value of #2 for each >>> string, which I presumably do by the same method as above to extract >>> all string1 (or ...2) and then use Map[] and Max[]. I would do this >>> all >>> with For loops (revealing my lack of Mathematica chops :-) ) but I'd >>> really like to learn how to do this sort of extraction in a >>> Mathematica-y way. Any help would be greatly appreciated! >> >> Let's say you want to know the maximum integer that occurs in slot #2 >> for all of the data that contain string3. >> >> In[4]:= >> Max[Part[#,2]&/@Cases[data,{_Integer,_Integer, string3,_,_}]] >> >> Out[4]= >> 3 >> >> This code extracts the second part from all of the list elements that >> match {_Integer, _Integer, string3, _,_} and finds the maximum value >> thereof. >> -- >> Curt Fischer >> > > > > -- DrBob at bigfoot.com www.eclecticdreams.net

**References**:**Re: Using Select with arrays? (Relative newbie)***From:*Curt Fischer <tentrillion@gmail.NOSPAM.com>

**Re: Re: Using Select with arrays? (Relative newbie)***From:*Hugo Mallinson <hfm21@cam.ac.uk>