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PONumPy: load heterogenous columns of data from list of strings
 

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    <p>I'm working with array data stored in an ASCII file (similar to <a href="http://thread.gmane.org/gmane.comp.python.numeric.general/42342" rel="nofollow">this thread</a>). My file is at least 2M lines (158 MB), and is divided into multiple sections with different schemas. In my module to read the format, I want to read the whole file via <code>lines = open('myfile.txt', 'r').readlines()</code>, so I can index the positions of each section, then read each section that I need into NumPy data structures.</p> <p>For example, one excerpt of a section is:</p> <pre><code>&gt;&gt;&gt; print lines[5:10] [' 1 0.1000 0.300E-03 0.000E+00 0.300E-03 0.000E+00 0.000E+00 0.300E-03 0.100E-03\n', ' 2 0.1000 0.120E-02 0.000E+00 0.120E-02 0.000E+00 0.000E+00 0.120E-02 0.100E-03\n', ' 3 0.1000 0.100E-02 0.000E+00 0.100E-02 0.000E+00 0.000E+00 0.100E-02 0.100E-03\n', ' 4 0.1000 0.110E-02 0.000E+00 0.110E-02 0.000E+00 0.000E+00 0.110E-02 0.100E-03\n', ' 5 0.1000 0.700E-03 0.000E+00 0.700E-03 0.000E+00 0.000E+00 0.700E-03 0.100E-03\n'] </code></pre> <p>Which has the schema <code>[int, float, float, float, float, float, float, float, float]</code>, and a later part will have have a simpler <code>[int, float]</code> schema:</p> <pre><code>&gt;&gt;&gt; print lines[20:25] [' 1 0.00000E+00\n', ' 2 0.43927E-07\n', ' 3 0.44006E-07\n', ' 4 0.44020E-07\n', ' 5 0.44039E-07\n'] </code></pre> <p>How can I quickly load in different sections of the lines with NumPy? I see there is <code>np.loadtxt</code>, but it requires a file handle, and reads all the way to the end. I also see <code>np.from*</code> functions, but I'm not sure how to use them with my already read <code>lines</code>. Do I need to read the file twice?</p> <p>With regards to the heterogeneous data types, I figure I can use a compound <code>dtype</code>, like <code>np.dtype([('col1', '&lt;i2'), ('col2', 'f4'), ('col3', 'f4'), ('col4', 'f4'), ('col5', 'f4'), ('col6', 'f4'), ('col7', 'f4'), ('col8', 'f4'), ('col9', 'f4')])</code>, correct?</p>
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