Using Select

• To: mathgroup at smc.vnet.net
• Subject: [mg76162] Using Select
• From: Mark Coleman <mark at markscoleman.com>
• Date: Thu, 17 May 2007 05:54:35 -0400 (EDT)

```Greetings,

I'm working on a small application and I'm searching for a way to
Select a subset of rows from a list based upon a list of criteria
chosen by the user.  Here is small (hypothetical) example. Say one
has a data set of consisting of a list of as follows:

{ {1,A,Blue,"Hello",10.5},{7,D,Green,"Goodbye",9.4},
{6,S,Yellow,"Hello",6.9},{3,A,Blue,"Hello",8.0}....}

The user will specify a letter and a color and the program should
Select[ ] the appropriate rows, e.g., if I pick Color=Blue and Letter
= A, then it will return

{ {1,A,Blue,"Hello",10.5},{3,A,Blue,"Hello",8.0}....}, etc.  Thus one
can enter Select[myData,(#[[2]]==A && #[[3]]==Blue)&] and get the
appropriate records.Note that The actual data set has about 20,000
records (lists), each with about 20 fields, and can select 7 or 8
different attributes, so the Select statements get fairly long.

My question involves an efficient way to code the Select statement if
a user wants to chose records that correspond to any value of a
particular field, e.g., All of the Color=Blue, regardless of the
Letter choice,e.g.,

Select[myData,(#[[3]]==Blue)&]

More precisely, is there a way to pass Select the user choice of any
letter using some sort of 'wildcard' value that represents any value
for the specific attribute, i.e.,

Select[myData,(#[[2]]=='Wildcard' && #[[3]]==Blue)&]

My motivation is that if I have may possible selection criteria, I
can still use a single Select statement.

Thanks,

-Mark

```

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