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 >