在Python中从文件读取数据块 [英] Reading data blocks from a file in Python

问题描述

我是python的新手，正在尝试从文件中读取数据的块".该文件的写法类似于:

I'm new to python and am trying to read "blocks" of data from a file. The file is written something like:

# Some comment
# 4 cols of data --x,vx,vy,vz
# nsp, nskip =           2          10


#            0   0.0000000


#            1           4
 0.5056E+03  0.8687E-03 -0.1202E-02  0.4652E-02
 0.3776E+03  0.8687E-03  0.1975E-04  0.9741E-03
 0.2496E+03  0.8687E-03  0.7894E-04  0.8334E-03
 0.1216E+03  0.8687E-03  0.1439E-03  0.6816E-03


#            2           4
 0.5056E+03  0.8687E-03 -0.1202E-02  0.4652E-02
 0.3776E+03  0.8687E-03  0.1975E-04  0.9741E-03
 0.2496E+03  0.8687E-03  0.7894E-04  0.8334E-03
 0.1216E+03  0.8687E-03  0.1439E-03  0.6816E-03


#          500  0.99999422


#            1           4
 0.5057E+03  0.7392E-03 -0.6891E-03  0.4700E-02
 0.3777E+03  0.9129E-03  0.2653E-04  0.9641E-03
 0.2497E+03  0.9131E-03  0.7970E-04  0.8173E-03
 0.1217E+03  0.9131E-03  0.1378E-03  0.6586E-03

and so on

现在，我希望能够指定和读取许多块中的仅一个数据块.我正在使用numpy.loadtxt('filename',comments='#')读取数据，但它一次加载了整个文件.我在网上搜索，有人为numpy io例程创建了一个补丁，以指定读取块，但它不在主流numpy中.

Now I want to be able specify and read only one block of data out of these many blocks. I'm using numpy.loadtxt('filename',comments='#') to read the data but it loads the whole file in one go. I searched online and someone has created a patch for the numpy io routine to specify reading blocks but it's not in mainstream numpy.

在gnuplot中选择数据块要容易得多，但是我必须编写例程来绘制分布函数.如果我能弄清楚读取特定的块，那么在python中会容易得多.另外，我还将所有可视化代码从IDL和gnuplot移至python，因此最好将所有内容都包含在python中，而不是将它们分散在多个包中.

It's much easier to choose blocks of data in gnuplot but I'd have to write the routine to plot the distribution functions. If I can figure out reading specific blocks, it would be much easier in python. Also, I'm moving all my visualization codes to python from IDL and gnuplot, so it'll be nice to have everything in python instead of having things scattered around in multiple packages.

我考虑过要从python中调用gnuplot，将一个块绘制到一个表中，然后将输出分配给python中的某个数组.但是我仍在开始，我不知道该怎么做.

I thought about calling gnuplot from within python, plotting a block to a table and assigning the output to some array in python. But I'm still starting and I could not figure out the syntax to do it.

任何想法，解决这个问题的指针都会有很大帮助.

Any ideas, pointers to solve this problem would be of great help.

推荐答案

快速入门:

>>> def read_blocks(input_file, i, j):
    empty_lines = 0
    blocks = []
    for line in open(input_file):
        # Check for empty/commented lines
        if not line or line.startswith('#'):
            # If 1st one: new block
            if empty_lines == 0:
                blocks.append([])
            empty_lines += 1
        # Non empty line: add line in current(last) block
        else:
            empty_lines = 0
            blocks[-1].append(line)
    return blocks[i:j + 1]

>>> for block in read_blocks(s, 1, 2):
    print '-> block'
    for line in block:
        print line


-> block
 0.5056E+03  0.8687E-03 -0.1202E-02  0.4652E-02
 0.3776E+03  0.8687E-03  0.1975E-04  0.9741E-03
 0.2496E+03  0.8687E-03  0.7894E-04  0.8334E-03
 0.1216E+03  0.8687E-03  0.1439E-03  0.6816E-03
-> block
 0.5057E+03  0.7392E-03 -0.6891E-03  0.4700E-02
 0.3777E+03  0.9129E-03  0.2653E-04  0.9641E-03
 0.2497E+03  0.9131E-03  0.7970E-04  0.8173E-03
 0.1217E+03  0.9131E-03  0.1378E-03  0.6586E-03
>>> 

现在我想你可以使用numpy读取行了...

Now I guess you can use numpy to read the lines...

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