How to write a Python loop to convert a large amount of coordinates into the GeoJSON LineString format?

Question

I reconstructed my dataset in pandas DataFrame by using a multi-index, and it is now in the following format.

In [1]: df.head(12)
Out [1]:

In order to put it into a GeoJSON LineString format and visualize it on a map, I need to write a Python loop over each point and each line through millions of satellite observational points. For reference, the following example specifies a GeoJSON LineString.

{ type: "LineString", coordinates: [ [ 40, 5 ], [ 41, 6 ] ] }

However, not always as shown in the figure that a line consists of 4 points for the first three lines, the number of points for a specific line in this dataset is totally random, ranging from 4 to hundreds.

I am so confused how to write a Python loop that could help me put my coordinates into GeoJSON LineString type by using a multi-index, e.g.

In [2]: df.Longitude[1][4]
Out [2]: 128

Thanks for your time!

Answer 1

A combination of groupby and to_json seems to work well.

import pandas as pd
import numpy as np
import pprint

arrays = [np.array([1, 1, 1, 2, 2, 3, 3, 3, 3, 3, 4, 4]),
          np.array([1, 2, 3, 1, 2, 1, 2, 3, 4, 5, 1, 2])]

df = pd.DataFrame(np.arange(24).reshape(12,2), 
                  index=arrays, columns=['Longitude', 'Lattitude'])

dd = {"type":"Feature", 
      "geometry":{"type":"Linestring",
                  "coordinates":None
                 },
      "properties":{"prop0":'red',
                    "prop1":'dashed'
                   }
     }

for _, group in df.groupby(level=0):
    dd["geometry"]["coordinates"] = group.to_json(orient='values')
    pprint.pprint(dd)

output:

{'geometry': {'coordinates': '[[0,1],[2,3],[4,5]]',
              'type': 'Linestring'},
 'properties': {'prop0': 'red',
                'prop1': 'dashed'},
 'type': 'Feature'}
{'geometry': {'coordinates': '[[6,7],[8,9]]',
              'type': 'Linestring'},
 'properties': {'prop0': 'red',
                'prop1': 'dashed'},
 'type': 'Feature'}
{'geometry': {'coordinates': '[[10,11],[12,13],[14,15],[16,17],[18,19]]',
              'type': 'Linestring'},
 'properties': {'prop0': 'red',
                'prop1': 'dashed'},
 'type': 'Feature'}
{'geometry': {'coordinates': '[[20,21],[22,23]]',
              'type': 'Linestring'},
 'properties': {'prop0': 'red',
                'prop1': 'dashed'},
 'type': 'Feature'}