Re: making a column into a list
- To: mathgroup at smc.vnet.net
- Subject: [mg22990] Re: [mg22964] making a column into a list
- From: "Allan Hayes" <hay at haystack.demon.co.uk>
- Date: Sun, 9 Apr 2000 01:45:53 -0400 (EDT)
- References: <8cnv2d$5bb@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Mark:
You report
> To get a column from a matrix in list form:
> IN>
> matrix = {{1, 2}, {1, 2}, {1, 2}}
> column = Column[matrix, 1]
> OUT>
> {{1, 2}, {1, 2}, {1, 2}}
> {1, 1, 1}
This doesn't work for me with Mathematica 4.0.
matrix = {{1, 2}, {1, 2}, {1, 2}}
column = Column[matrix, 1]
{{1, 2}, {1, 2}, {1, 2}}
Column[{{1, 2}, {1, 2}, {1, 2}}, 1]
Did you mean TakeColumns from the package?
<< LinearAlgebra`MatrixManipulation`
TakeColumns[matrix, {1}]
{{1}, {1}, {1}}
-------------------------------------
But in Mathematica 4.0 we can use
matrix[[All, {1}]]
{{1}, {1}, {1}}
And this is much faster:
matrix = Table[Random[], {50000}, {10}];
TakeColumns[matrix, {1}]; // Timing
{1.37 Second, Null}
matrix[[All, {1}]]; // Timing
{0.11 Second, Null}
--
Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565