Export, Import, Convert Types Again?
- To: mathgroup at smc.vnet.net
- Subject: [mg57193] Export, Import, Convert Types Again?
- From: Lee Newman <leenewm at umich.edu>
- Date: Fri, 20 May 2005 04:43:32 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Q: What is the (best) way to save a big expression of data to be used
later in the same notebook without having to do type conversion processing?
Situation:
1) I have a notebook that imports data from various Excel spreadsheets
and converts the data to the desired types. When complete, I "save" the
expression containing the data using Export, i.e,
Export["featureDB.tsv", "TSV"]. I do this so I don't have to re-process
the data everytime I do analysis on it in this notebook.
2) When I open the noteobook again, I import the data using the
statement: featureDB = Import["featureDB.tsv"]
Problem:
Many of type conversions that I took the time to process are lost.
Using Head /@ featureDB[[1]] before and after the export/re-import, the
types are as follows:
Before: {Integer, Integer, List, List, List, Integer, List, List,
Symbol, List}
After : {Integer, Integer, String, String, String, Integer, String,
String, String, String}
So it seems that lists become Strings as Symbols (e.g. True, False,
Null). I use Export so I can view the data outside Mathematica using a text
editor -- should I use Save instead? Is there another Export format
that will preserve mathematica expressions like lists upon Import?
Thanks,
Lee