Databases
StackOverflow2013
Postsdbo
PORead large amount of ASCII numbers and write in binary form
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PORead large amount of ASCII numbers and write in binary form
    primarykey
    data
    text
    <p>I have data files with about 1.5 Gb worth of floating-point numbers stored as ASCII text separated by whitespace, e.g., <code>1.2334 2.3456 3.4567</code> and so on.</p> <p>Before processing such numbers I first translate the original file to binary format. This is helpful because I can choose whether to use <code>float</code> or <code>double</code>, reduce file size (to about 800 MB for <code>double</code> and 400 MB for <code>float</code>), and read in chunks of the appropriate size once I am processing the data.</p> <p>I wrote the following function to make the ASCII-to-binary translation:</p> <pre><code>template&lt;typename RealType=float&gt; void ascii_to_binary(const std::string&amp; fsrc, const std::string&amp; fdst){ RealType value; std::fstream src(fsrc.c_str(), std::fstream::in | std::fstream::binary); std::fstream dst(fdst.c_str(), std::fstream::out | std::fstream::binary); while(src &gt;&gt; value){ dst.write((char*)&amp;value, sizeof(RealType)); } // RAII closes both files } </code></pre> <p>I would like to speed-up <code>acii_to_binary</code>, and I seem unable to come up with anything. I tried reading the file in chunks of 8192 bytes, and then try to process the buffer in another subroutine. This seems very complicated because the last few characters in the buffer may be whitespace (in which case all is good), or a truncated number (which is very bad) - the logic to handle the possible truncation seems hardly worth it.</p> <p>What would you do to speed up this function? I would rather rely on standard C++ (C++11 is OK) with no additional dependencies, like boost.</p> <p>Thank you.</p> <h1>Edit:</h1> <p>@DavidSchwarts:</p> <p>I tried to implement your suggestion as follows:</p> <pre><code> template&lt;typename RealType=float&gt; void ascii_to_binary(const std::string&amp; fsrc, const std::string&amp; fdst{ std::vector&lt;RealType&gt; buffer; typedef typename std::vector&lt;RealType&gt;::iterator VectorIterator; buffer.reserve(65536); std::fstream src(fsrc, std::fstream::in | std::fstream::binary); std::fstream dst(fdst, std::fstream::out | std::fstream::binary); while(true){ size_t k = 0; while(k&lt;65536 &amp;&amp; src &gt;&gt; buffer[k]) k++; dst.write((char*)&amp;buffer[0], buffer.size()); if(k&lt;65536){ break; } } } </code></pre> <p>But it does not seem to be writing the data! I'm working on it...</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USEscualo
    1. USEscualo
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. PORead large amount of ASCII numbers and write in binary form
      1. USBen Voigt
      1. VTFavorite
    2. VO
      singulars
      1. PORead large amount of ASCII numbers and write in binary form
      1. USDanil Asotsky
      1. VTFavorite
    1. CODo you mean to say reduces the file size to 800 *M*B not 800 *G*B?
      singulars
      1. PORead large amount of ASCII numbers and write in binary form
      1. USDan F
    2. COI think you'll find that using a classic C `FILE *` and `fscanf()` will be a fair bit faster than using `fstream`. [Also don't think you should be using `fstream::binary` on your input file - it probably doesn't make any difference to performance, but correctness will be affected.
      singulars
      1. PORead large amount of ASCII numbers and write in binary form
      1. USMats Petersson
    3. CO@DanF -- yes. Thank you!
      singulars
      1. PORead large amount of ASCII numbers and write in binary form
      1. USEscualo
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload