Re: simple newbee questions
- To: mathgroup at smc.vnet.net
- Subject: [mg29546] Re: [mg29518] simple newbee questions
- From: BobHanlon at aol.com
- Date: Sun, 24 Jun 2001 02:00:59 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
In a message dated 2001/6/23 2:07:47 AM, wzn at jongnederland.nl writes: >How can I calculate the mean of a matrix (n*m), an array works fine... > >How can I select an area in a matix? > m = Array[a, {2, 3}]; The means by row (Plus@@#)/Length[#]& /@ m {(1/3)*(a[1, 1] + a[1, 2] + a[1, 3]), (1/3)*(a[2, 1] + a[2, 2] + a[2, 3])} The means by column (Plus@@#)/Length[#]& /@ Transpose[m] {(1/2)*(a[1, 1] + a[2, 1]), (1/2)*(a[1, 2] + a[2, 2]), (1/2)*(a[1, 3] + a[2, 3])} The mean of all elements (Plus@@#)/Length[#]&[Flatten[m]] (1/6)*(a[1, 1] + a[1, 2] + a[1, 3] + a[2, 1] + a[2, 2] + a[2, 3]) m = Array[a, {8, 10}]; If you want the intersection of rows (4 - 6) with columns (2 - 5) m[[Range[4, 6], Range[2, 5]]] Bob Hanlon Chantilly, VA USA