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Using ReadList to read a string

  • To: mathgroup at smc.vnet.net
  • Subject: [mg83781] Using ReadList to read a string
  • From: Donald DuBois <donabc at comcast.net>
  • Date: Fri, 30 Nov 2007 05:23:38 -0500 (EST)

Hello,

I am trying to get ReadList to read a string in a text file  (filename.txt).

I would like NOT to have use Import because it is MUCH slower in reading
a text file than ReadList is.  For example:

(1) a file with 50,000 records can be created
(2) Exported  to disk 
(3) read by ReadList[...] and 
(4) read by Import[...]


dataFile1 = 
 Table[{2001, "nameA", "symbolA", 
   15.5}, {50000}]; Export["out1.txt", dataFile1, "Table"];

AbsoluteTiming[
 out1ReadList = ReadList["out1.txt", {Number, Word, Word, Number}];]

AbsoluteTiming[out1Import = Import["out1.txt", "Table"];]

{0.1718750, Null}

{2.4375000, Null}

Import takes 14 times longer to read in the same file as compared to ReadList.
So, naturally, I would like to use ReadList whenever I have a .txt file to be read in from disk.

However, the file to be read  is slightly more complicated than the one above (out1.txt).  
There is a string that is added to the file as the second element of a record.
The first few records of the file (EWZ2.TXT below)  look like the following with each record
consisting of eight elements: a number, string, word followed by five integer numbers for each record.  
Each record is on a separate line.  

EWZ2.TXT:

20000714 "iShares MSCI Brazil Index" EWZ      250        1627        1637        1627        1637
20000717 "iShares MSCI Brazil Index" EWZ      100        1730        1735        1730        1735
20000718 "iShares MSCI Brazil Index" EWZ      100        1730        1730        1730        1730
20000719 "iShares MSCI Brazil Index" EWZ      100        1686        1686        1686        1686
20000720 "iShares MSCI Brazil Index" EWZ       50        1724        1724        1724        1724

The format of the above file is: {Number, String, Word, Number, Number, Number, Number, Number}

If this file on disk is named "EWZ2.TXT" I am not able to use ReadList to read it.
I use two format specifications within ReadList
and neither of them works: 

{Number, String, Word, Number, Number, Number, Number, Number}
and {Number, Word, Word, Number, Number, Number, Number, Number}.

ReadList["EWZ2.TXT", {Number, String, Word, Number, Number, Number, 
  Number, Number}]
ReadList["EWZ2.TXT", {Number, Word, Word, Number, Number, Number, 
  Number, Number}]



{{20000714, 
  " \"iShares MSCI Brazil Index\" EWZ      250        1627        \
1637        1627        1637", "20000717", $Failed, EndOfFile, 
  EndOfFile, EndOfFile, EndOfFile}}

{{20000714, "\"iShares", "MSCI", $Failed, EndOfFile, EndOfFile, 
  EndOfFile, EndOfFile}}


Using "String" for the format of the second element seems to have more success than "Word" but, when
read, none of the elements is separated by a comma as happened when using ReadList to read
out1.txt above.

"iShares MSCI Brazil Index" should be the second element of a sublist within
the entire list (Table) and EWZ  (with or without quotes) should be the third element
within a sublist.

The defintion of a String in the function description for ReadList is
"string terminated by a newline" which does not describe the above file.
 (EWZ2.TXT).  If the string is moved in the file so that it is the last item 
 in any record, such as
 
 20000714  EWZ      250        1627        1637        1627        1637  "iShares MSCI Brazil Index"

then a format of {Number, Word, Number, Number, Number, Number, Number, String} 
in ReadList DOES work to read the file correclty.

But, is there anyway to get ReadList to read the above file (EWZ2.TXT) with the string
as the second item of a record so that the speed advantage of ReadList over Import
can be retained? 

Or is there some other function I should be using other than Import and/or ReadList?

Thank you in advance for any help you can give me.  
Don


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