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MathGroup Archive 2005

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Re: Controlling program flow across cells

  • To: mathgroup at smc.vnet.net
  • Subject: [mg54391] Re: Controlling program flow across cells
  • From: David Bailey <dave at Remove_Thisdbailey.co.uk>
  • Date: Sun, 20 Feb 2005 00:07:50 -0500 (EST)
  • References: <cv6s3v$6l2$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

semiclassical wrote:
> Here is the problem:
> 
> I import a large data file - 20 years of hourly observations, which is
> used to populate a raw data list of approximately 176,000 rows with
> the following structure:
>     
> {year, day, hour, validity_Flag, data_Item1, ... ,data_Item5}
> 
> The list is then parsed, filtered and operated upon in several
> different ways. In particular I calculate statistical properties of a
> specified 5 year period. The process is encapsulated in a number of
> cells-
> 
> Cell_1 : Parse[ Import and filter raw data ];
> 
> Cell_2a: Parse[ Chip out and sort period of interest ];
> Cell_2b: Calculate[ statistical properties of validity_Flag ];
> Cell_2c: Calculate[ statistical properties of data_Item ];
> Cell_2d: Calculate[ distribution of data_Item ];
> 
> This is done for most data_Items, additionally calculations are made
> for hourly statistics and quartely statistics. Now what I would like
> to be able to do is loop over the four 5 year periods within the
> complete 20 year span. Here are two questions:
> 
> 1. I would like to set up a For[] loop across Cell_2a-Cell_2d to loop
> through the four periods of interest. How can I do this, or should I
> actually have built the program in a different way?
> 
> 2. How can I get output from within a For[] loop as it is executing?
> For example, I might like to watch some value of a given variable
> within the loop as it is calculated (in C I would use a printf). 
> 
> Thanks,
> 
> Aaron
> semiclassical at hotmail.com
> 

Your question is a little vague, so I am going to guess what I think you 
mean.

I take it each of these four cells contains a calculation. The first 
step is to change each of these into a function definition:

step1[]:= (........)

step2[x_]= (........)

etc.

I will assume that you have set things up so that the output of each 
calculation is the input to the next, so one turn of your loop would
become step4[step3[step2[step1[]]]]

Note that step1 does not need an argument since it reads its data from a 
file. Maybe each of your steps leaves its output in variables, in which 
case all the functions would be defined with no arguments, and you would 
use step1[];step2[];step3[];step4[]

Here is the loop to repeat the operations.


For[i = 1, i < 176000, step4[step3[step2[step1[]]]]; i++]

The equivalent of C's printf is Print - you can use any number of 
arguments including strings, and you dont need to bother with a format.

In general, I would say, think in terms of function definitions - as you 
would in C - not in terms of cells.

BTW, I think you would find that a short Mathematica course would help 
you enormously.

David Bailey
dbaileyconsultancy.co.uk


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