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I want to quantify the saving of space I can get by changing the format of a file.

I have a sparse matrix stocked in a text file (30% sparsity). Columns are separated by tabs.

Following an idea in an SO answer, I will change the format to row_id, col_id for the non zero terms only. I know how much space a float takes, but my question is: how much space does a tab take?

Community
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bigTree
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  • How much bytes a tab character uses in a text file depends on the character encoding. The ASCII character takes one byte: `\t`. Note that an editor may display a tab character as 2 or 4 spaces, or whatever is configured. – CouchDeveloper Feb 14 '14 at 10:39

2 Answers2

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1 byte, but significantly less if you're using compression (based on how common they will be, less than a bit on average). Use compression.

U2EF1
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CouchDeveloper in his comment is correct. It's impossible to tell from the data you provide.
In a single byte character set encoding you'd save 1 byte per separator from the current ", ".
In a multibyte encoding it'd depend on the way each of those characters is encoded, you could theoretically even lose space. Say a tab is encoded as 4 bytes, a comma and space as 1 each, you'd end up taking 2 more bytes per separator.
Unless you have many separators and relatively very little data, I'd not worry one way or another, it'd be micro optimisation.
If you do, a binary encoding scheme might be more relevant.

jwenting
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