python: sort coordinates in csv file

Question

I have set of three dimensional coordinates in csv file, like: [two first columns are respectively latitude and longitude in decimal degrees, third one is elevation]

49.000000,14.000000,47.206
55.000000,14.000000,34.727
49.000000,24.366667,31.979
55.000000,24.366667,24.744

I would like to sort the coordinates in the following order: starting from north-west corner then go east-south, like:

55.000000,14.000000,34.727
55.000000,24.366667,24.744
49.000000,14.000000,47.206
49.000000,24.366667,31.979

Elevation has to be kept, glued to given 2D coordinates.

I tried simple descending 1st column and ascending 2nd column but got no desired order.

import csv

coordinates = [];

file_in = csv.reader(open('NewFile.csv', 'rb'), delimiter=',', quotechar='|');
file_out = '11dataout.txt'
fout=open(file_out,"w")

for row in file_in:
    coordinates.append(row)
coordinates.sort(key=lambda x: x[1], reverse=True)                              
coordinates.sort(key=lambda x: x[2])
fout.write(str(coordinates))
fout.write('\n')

Thanks in advance.

Answer 1

您也可以一次性进行排序：

coordinates.sort(key = lambda x: (-x[0], x[1]))

Answer 2

You problem is that you assume lists are 1-indexed, when they aren't:

[55.000000, 14.000000, 34.727]
#0          1          2

Also, you sort in the wrong order, you need to sort by longitude then latitude:

coordinates.sort(key=lambda x: x[1])                              
coordinates.sort(key=lambda x: x[0], reverse=True)