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Re: Histogram ignores 'bspec' (bin spec) ??

  • To: mathgroup at smc.vnet.net
  • Subject: [mg126761] Re: Histogram ignores 'bspec' (bin spec) ??
  • From: "Nasser M. Abbasi" <nma at 12000.org>
  • Date: Tue, 5 Jun 2012 04:53:33 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <jqhr60$klr$1@smc.vnet.net>
  • Reply-to: nma at 12000.org

On 6/4/2012 3:21 AM, James Stein wrote:
> I would like to plot a histogram with a fixed number of bars, e.g. ten bars.
> Consider this code:
>
> SeedRandom [ 1 ] ;
> foo = RandomVariate [ NormalDistribution [ 0, 1], 1000 ] ;
> baz = Table [ Histogram [ foo, k ], { k, 8, 15 } ] ;
> 1 == Length [ DeleteDuplicates [ baz ] ]
>
> The last line prints 'True', confirmed by visual inspection of baz which
> reveals eight identical histograms, each containing 13 bins. What do I fail
> to understand here?
>
>

I am not sure why the same bins show up each time.

But the way I would do this, at least for now, is to
use {dx} and not n for bspec.  This way I know exactly
the bin width I want to use.  Something like this

-----------------------
SeedRandom[1];
foo = RandomVariate[NormalDistribution[0,1],1000];
max = Max[foo];
min = Min[foo];
wid = max-min;
baz = Table[Histogram[foo,{wid/(k-1)},"PDF"],{k,8,15}]
----------------------

I used PDF above just to get the total area =1 that is all.
It is not needed otherwise.

now

1 == Length[DeleteDuplicates[baz]]

gives False. Note that total width of the data is less
than 8 (99.9999% of the time, i.e. 4 standard deviations each
side gives 4. So data goes from -4 to 4 since you
used  NormalDistribution with zero mean and std=1).

Not sure if Mathematica has used '1' for the width of
each bin when using just 'n'.

So 8 bins or more will result in the same
data being binned into only first 8 bins (anything
over 8 bins will have zero elements, hence might not
show in the plot). This might explain why all plots
has 8 bins.

Not sure. But either way, using {dx} seems safer
until some expert here can explain this better.

--Nasser








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