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MathGroup Archive 1998

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Re: config. data from internet database

  • To: mathgroup at smc.vnet.net
  • Subject: [mg14747] Re: config. data from internet database
  • From: paulh (P.J. Hinton)
  • Date: Thu, 12 Nov 1998 02:17:45 -0500
  • Organization: Wolfram Research, Inc.
  • References: <72beid$k2c@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In article <72beid$k2c at smc.vnet.net>, jim leddon <jleddon at cyberramp.net>
writes:

|> I have a question regarding how to extract and put into a list form, 
|> numbers from an internet science database file that I have already 
|> imported into my Mathematica 3.0 program using "ReadList". The
problem  |> is as follows:
|> 
|> I want to extract from a file named "1997.ADJ" (which is a list of
daily |> 10.7 cm solar flux values for the year 1997), certain columns
of |> numbers  from the period Sept. 1, 1997 to Dec. 31, 1997 which
will form |> a list  (time series) which I will use to plot, get a
Fourier |> Transform, a  power-spectrum, etc..  |> The file comes from
the internet site:   |> http://www.ngdc.noaa.gov/stp/stp.html and is
found after getting into  |> this site by the following steps: |> 
|> Click "Solar and Upper Atmosph."
|> Click "Get Data"
|>  ""     "Solar Radio"
|>  ""      " Flux"
|>   ""     "1997.ADJ"
|> 
|> I am at this point where I have read in the file by using the
ReadList  |> function as follows:  ReadList["a\1997.adj", String] My
output is a |> table of average daily values for each month of 1997
with  a header and |> footer section containing comments. I only want
to extract the data |> values from four columns (Sep., Oct., Nov, Dec).
I've tried using  |> mathematica functions such as MemberQ,
Character,and  Select and have |> not been successful.  At this point,
I'd really  appreciate some help! |> Got any ideas?
|> 
|> Thanks for your time and consideration. I look forward to hearing
from  |> you.

Because this table is slightly irregular, we'll have to do some fancy
footwork to get the data you need:

(* First, let's open the file as an InputStream[]. *)

In[1]:= stmp = OpenRead["1997.ADJ"];

(* Skim past the five header lines. *)

In[2]:= Do[Read[stmp, String], {5}]

(* Now read in the 37 lines of data and and vertical spaces. *)

In[3]:= daysString = Table[Read[stmp, String], {37}];

(* Then we map a function which converts each string into a stream and
   breaks the strings up into lists of individual strings. *)

In[4]:= daysTable = Map[Block[{stmp = StringToStream[#], lst}, 
           lst = ReadList[stmp, Word]; Close[stmp]; lst]&, daysString];

(* Close the data file. *)

In[5]:= Close[stmp];

(* Any vertical spaces will produce empty lists, so we can throw
   those out. *)

In[6]:= trimmedTable = DeleteCases[daysTable, {}];

(* Now we even out the array be entering rows 29 and 30 of Febrary. *)

In[7]:= MapAt[Insert[#1, 0, 3] & , %, 29];

In[8]:= MapAt[Insert[#1, 0, 3] & , %, 30];

(* And do the same for day 31 of September, April, June, and November.
*)

In[8]:= finalTable = MapAt[ReplaceAll[#, 
         {date_, jan_, mar_, may_, jul_, aug_, oct_, dec_} -> 
           {date, jan, 0, mar, 0, may, 0, jul, aug, 0, oct, 0, dec}]&,
             %, 31]

(* We can now get the last four columns and knock out the zero pads. *)

In[9]:= desiredData = Map[Map[ToExpression, #]&, 
          DeleteCases[Take[Transpose[finalTable], -4], 0, -1]]

(* The nested Map operation is needed to turn the strings into numbers.
*)

Hope that helps.

--
P.J. Hinton	
Mathematica Programming Group		paulh at wolfram.com Wolfram Research,
Inc.			http://www.wolfram.com/~paulh/ Disclaimer: Opinions expressed
herein are those of the author alone.


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