使用python从.txt文件中检索数据？

Question

In the following you can see data from a ephemeris.txt file. Now I want to retrieve several columns(say, for example the column starting with 00:00, 27.69 and 44.1) and name the array as x,y,z. What do I have to do?

I tried this

x, y, z = numpy.loadtxt("ephemeris.txt", unpack=True)

And this get this error

"ValueError: could not convert string to float: Date__(UT)__HR:MN"

Could you also help me in converting that HR:MN into minute only?

Date__(UT)__HR:MN     R.A.__(a-apparent)__DEC\
**********************************************\
 2013-Jan-01 00:00 *   14 31 27.69 -12 29 44.1\
 2013-Jan-01 00:01 *   14 31 27.71 -12 29 44.1\
 2013-Jan-01 00:02 *   14 31 27.72 -12 29 44.2\
 2013-Jan-01 00:03 *   14 31 27.73 -12 29 44.2\
 2013-Jan-01 00:04 *   14 31 27.75 -12 29 44.3\
 2013-Jan-01 00:05 *   14 31 27.76 -12 29 44.3\
 2013-Jan-01 00:06 *   14 31 27.77 -12 29 44.4\
 2013-Jan-01 00:07 *   14 31 27.78 -12 29 44.4\
 2013-Jan-01 00:08 *   14 31 27.80 -12 29 44.4\
 2013-Jan-01 00:09 *   14 31 27.81 -12 29 44.5\

thanks in advance

Answer 1

You can use some more arguments of the loadtxt function.

The error you are getting most probably is due to the first two header lines, so skip them with the skiprows=2 argument;

Also, each row contains data in a different format, separated by space. Use delimiter=' ' just in case, and you can opt between dtype=string and dtype=object .

a = numpy.loadtxt("ephemeris.txt", delimiter=' ', dtype=string, skiprows=2)

This should give you a single array from where you can perform many kinds of "conversions": split one array per column, create a list of rows, etc.

x,y,z,etc = numpy.hsplit(a, a.shape[1])
x = x.astype(datetime)

# or
x = a[:,0].astype(datetime)
y = a[:,1].astype(some_type)

or something along these lines...

Hope this helps, and please elaborate more in the comments if needed.

Answer 2

import re
f = open("ephemeris.txt")
for line in f.readlines():
    r = re.search("(\d{4})\-(\w{3})-(\d{2}) (\d{2}):(\d{2}) \*   (.*?)\\\n", line)
    if r:
        print "Year: "+r.group(1)
        print "Month: "+r.group(2)
        print "Day: "+r.group(3)
        print "Hour: "+r.group(4)
        print "Minute: "+r.group(5)
        print "Data: "+r.group(6)

This will read every line of the file, check if it matches the pattern and if it does so, print all the data it could retrieve.

Answer 3

You can also split each line, setting a character separator. Then you can access on each (string) token using indexes:

def prova():
    f = open('/home/frenk/Desktop/ephemeris.txt')
    l = []
    for line in f:
        l = line.split(" ")
        print "date: " + l[1]

Second, if you want to convert a string like "31" to integer 31, you can simply write:

x = int('31')

Note that you can select a slice of string using slice notation:

string = "This is a slice of string"
print string[10:15]