如何从带有python中适当标签的文本文件中提取数字

Question

boundary
        layer 2
        datatype 0
        xy  15   525270 8663518   525400 8663518   525400 8664818   525660 8664818
                 525660 8663518   525790 8663518   525790 8664818   526050 8664818
                 526050 8663518   526180 8663518   526180 8665398   525980 8665598
                 525470 8665598   525270 8665398   525270 8663518
        endel

I have coordinates of polygons in this format shown above. Each polygon starts with "boundary" and ends with "endel". I am having trouble extracting the layer number, number of points, and the coordinates into either a numpy array or a pandas dataframe.

To be specific to this example, I need the layer number (2), number of points (15), and the xy coordinate pairs.

with open('source1.txt', encoding="utf-8") as f:
    for line in f:
        line = f.readline()
        srs= line.split("\t")
        print(srs)

Doing this doesnt split the numbers even thoe they are separated by tabs

['        layer 255\n']
['        xy   5   0 0   22800000 0   22800000 22800000   0 22800000\n']
['        endel\n']

This is the result i got with that

with open('source1.txt', encoding="utf-8") as f:
    for line in f:
        line = f.readline()
        srs= line.split(" ")
        print(srs)

This isnt what i wanted but i tried that too and yet got a bad split

['', '', '', '', '', '', '', '', 'layer', '255\n']
['', '', '', '', '', '', '', '', 'xy', '', '', '5', '', '', '0', '0', '', '', '22800000', '0', '', '', '22800000', '22800000', '', '', '0', '22800000\n']
['', '', '', '', '', '', '', '', 'endel\n']

I couldnt go to numpy part as im stuck in processing the string from the file

Edited as per request

Answer 1

You could use some trivial code such as:

res = []
coords = []
xy = False
with open('data.txt') as f:
    for line in f.readlines():
        if 'layer' in line:
            arr = line.split()
            layer = int(arr[-1].strip())
        elif 'xy' in line:
            arr = line.split()
            npoints = int(arr[1])
            coords = arr[2:]
            xy = True
        elif 'endel' in line:
            res.append([layer, npoints, coords[0:npoints]])
            xy = False
            coords = []
        elif xy:
            coords.extend(line.split())
print(res)

Then, you can convert the resulting list to numpy array, or whatever you like, but note that coords are still strings in the code above.

Answer 2

You can use a regex to parse that file into blocks of the relevant data then parse each block:

for block in re.findall(r'^boundary([\s\S]+?)endel', f.read()):
    m1=re.search(r'^\s*layer\s+(\d+)', block, re.M)
    m2=re.search(r'^\s*datatype\s+(\d+)', block, re.M)
    m3=re.search(r'^\s*xy\s+(\d+)\s+([\s\d]+)', block, re.M)
    if m1 and m2 and m3:
        layer=int(m1.group(1))
        datatype=int(m2.group(1))
        xy=int(m3.group(1))
        coordinates=[(int(x),int(y)) for x,y in zip(*[iter(m3.group(2).split())]*2)]
    else:
        print "can't parse {}".format(block)  

A variable number of coordinates are supported after the xy and it is trivial to test if the number of coordinates parsed is the number expected with len(coordinates)==xy .

As written, this requires reading the entire file into memory. If size is an issues, (and it usually is not for small to moderate size files), you can use mmap to make the file appear to be in memory.