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Re: Table extraction
*To*: mathgroup at smc.vnet.net
*Subject*: [mg19197] Re: [mg19141] Table extraction
*From*: BobHanlon at aol.com
*Date*: Tue, 10 Aug 1999 02:52:52 -0400
*Sender*: owner-wri-mathgroup at wolfram.com
Maurice,
mat = Array[a, {5, 4}];
As you indicated, extracting rows is straightforward.
mat[[3]]
{a[3, 1], a[3, 2], a[3, 3], a[3, 4]}
Part[mat, {1, 3}]
{{a[1, 1], a[1, 2], a[1, 3], a[1, 4]},
{a[3, 1], a[3, 2], a[3, 3], a[3, 4]}}
To extract columns, use Transpose
Transpose[{Transpose[mat][[3]]}]
{{a[1, 3]}, {a[2, 3]}, {a[3, 3]}, {a[4, 3]}, {a[5, 3]}}
Transpose[Part[Transpose[mat], {1, 3}]]
{{a[1, 1], a[1, 3]}, {a[2, 1], a[2, 3]}, {a[3, 1], a[3, 3]},
{a[4, 1], a[4, 3]}, {a[5, 1], a[5, 3]}}
Alternatively, you can use Column in the standard package DataManipulation
Needs["Statistics`DataManipulation`"]
Column[mat, 3]
{a[1, 3], a[2, 3], a[3, 3], a[4, 3], a[5, 3]}
Transpose[{%}]
{{a[1, 3]}, {a[2, 3]}, {a[3, 3]}, {a[4, 3]}, {a[5, 3]}}
Column[mat, {1, 3}]
{{a[1, 1], a[1, 3]}, {a[2, 1], a[2, 3]}, {a[3, 1], a[3, 3]},
{a[4, 1], a[4, 3]}, {a[5, 1], a[5, 3]}}
Bob Hanlon
In a message dated 8/6/99 5:29:34 AM, maurice at phas.ucalgary.ca writes:
>I am trying to extract a section of a table with not much luck....
>
>I have defined two tables (actually two arrays which are used to plot
>vectors with ListPlotVectorField) as follows:
>
>xyvector = Table[{0.,0.},{j,1,64},{i,1,320}];
>backvector = Table[{0.,0.},{j,1,16},{i,1,100}];
>
>I need to extract part of xyvector and place it into backvector. I have
>tried to use Part. I can extract the j range correctly (rows), but I
>can't get the Part function to extract in the i range (columns).
>
>I tried using Part[xyvector,{2,3}] which extracts 2 rows but I cannot
>figute out how to extract the necessary columns
>
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