Mathematica: how to read files?

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SUMMARY

This discussion focuses on reading data from two text files, map.txt and event.txt, using Mathematica. The provided code snippet demonstrates how to open and read the map.txt file, extract numerical data while omitting specific characters, and concatenate the results. Users are advised to ensure the correct file path for OpenRead and to be aware of potential issues with regular expressions affecting data formatting, particularly with exponential notation.

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  • Familiarity with Mathematica syntax and functions
  • Understanding of regular expressions in Mathematica
  • Basic knowledge of file handling in Mathematica
  • Experience with data formatting and parsing
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  • Explore Mathematica's RegularExpression function for advanced text manipulation
  • Learn about the ToExpression function in Mathematica for converting strings to expressions
  • Investigate file path management in Mathematica for efficient file access
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Data scientists, astrophysicists, and Mathematica users looking to efficiently read and process data from text files.

nenyan
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reading data from txt files
there are two .txt files. One is map.txt, another is event.txt.

map looks like below:

dfafdafskdjf:{{0.837711763427 -0.8359730469 2.4152891949e-04 0.000360245716236} {0.831761777387 -0.8240730748 2.4446745066e-04 0.000359914513716} {0.819861805217 -0.8062231165 2.4910805126e-04 0.000359863615611}} klsajlkf

What I need are data in {}, omited the begging srting and the endding string.


event.txt：
PGC | Name | RA | Dec | Type | App_Mag | Maj_Diam (a) | err_Maj_Diam | Min_Diam (b) | err_Min_Diam | b/a | err_b/a | PA | Abs_Mag | Dist | err_Dist | err_App_Mag | err_Abs_Mag |

2|UGC12889|0.00047|47.27450|3.1|13.31|1.546|0.498|1.314|~|0.85|0.100|~|-21.05|72.458|10.869|0.61|0.61|
4|PGC000004|0.00096|23.08764|5.0|15.39|0.851|0.078|0.186|~|0.219|0.015|~|-18.68|63.264|13.918|0.39|0.40|
...
...


How to read these two files by mathematica? Thanks.
 
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Perhaps this will get you started

In[1]:= stream=OpenRead["map.txt"];
allwords="";
While[(word=Read[stream,Record])=!=EndOfFile,
word=StringReplace[word,RegularExpression["[a-z:]*"]->""];
allwords=StringJoin[allwords,word];
];
Close[stream];
Print[allwords];

From In[1]:=
{{0.837711763427 -0.8359730469 2.4152891949-04 0.000360245716236} \
{0.831761777387 -0.8240730748 2.4446745066-04 \
0.000359914513716}{0.819861805217 -0.8062231165 2.4910805126-04 \
0.000359863615611}}

Now you will need to position your map.txt file in the appropriate place or you will have to give a path to the OpenRead.
Notice this has "eaten" your 'e' in your exponential form because the regular expression is eliminating alphabetic characters, and colons. But you would have needed to find a way to correctly translate your exponents into a Mathematica format anyway and this will just give you a little more practice. Notice you do not have commas between your }{ in your input and this will make it a little more difficult to have Mathematica easily translate this as a single simple expression using ToExpression.

This should give you an idea how to get started. Look up RegularExpression in Mathematica for more information. If you get stuck then show how much you have figured out and just where you are stuck and someone can provide more pointers.