Write coordinates of array of values in multidimensional array

Question

I have this list:

list = [[0, 5], [0, 3, 6], [1, 2, 4], [1, 7], [0, 1]]

Each element refers to a point with coordinates listed as two arrays:

Lon = [2.0,3.0,5.0,2.0,6.0,1.0,3.0,4.0]
Lat = [4.0,6.0,5.0,3.0,4.0,2.0,1.0,7.0]

I am trying to create an array that is in the following format:

[[Lon_0,Lat_0],[Lon_5,Lat_5]]
[[Lon_0,Lat_0],[Lon_3,Lat_3],[Lon_6,Lat_6]]
...

I tried the zip function but something is missing and I don't know how to move forward:

for m in list:
    for n in m:
        Coord = zip((Lon[n], Lat[n]))

Any help is appreciated

You don't need a for loop, just zip(Lon, Lat) and you're good. — Spice
– Spice, Commented Jun 12, 2018 at 14:12
just try zip(Lon, Lat). To turn it into a list use: list(zip(Lon, Lat)). — pask
– pask, Commented Jun 12, 2018 at 14:12
Oh and something to note is, that zip will turn the "inner" list into a tuple. eg: [(Lon_0, Lat_0), (...), ... ]. — pask
– pask, Commented Jun 12, 2018 at 14:14
Also, consider renaming your "list" from list to something else, say lst. By naming a variable list you override the list constructor. So, for example, @pask's previous suggestion will not work even though it should. — hilberts_drinking_problem
– hilberts_drinking_problem, Commented Jun 12, 2018 at 14:16
But the zip function is not subscriptable, how do I call the zipped coordinate of each point as in the list? — mb567
– mb567, Commented Jun 12, 2018 at 14:16

Cristian Ramon-Cortes · Accepted Answer · 2018-06-12 14:22:14Z

1

You can go through each index inside each element of your list and rebuild an entry with the Lon, Lat values.

Here is the code:

# Sample data
list = [[0, 5], [0, 3, 6], [1, 2, 4], [1, 7], [0, 1]]
Lon = [2.0,3.0,5.0,2.0,6.0,1.0,3.0,4.0]
Lat = [4.0,6.0,5.0,3.0,4.0,2.0,1.0,7.0]

# Construct result list
result = []                                                                                                                          
for entry in list:
    elem = []
    for index in entry:
        elem.append([Lon[index], Lat[index]])
    result.append(elem)

# Sample output
print(result)
[[[2.0, 4.0], [1.0, 2.0]], 
 [[2.0, 4.0], [2.0, 3.0], [3.0, 1.0]], 
 [[3.0, 6.0], [5.0, 5.0], [6.0, 4.0]], 
 [[3.0, 6.0], [4.0, 7.0]], 
 [[2.0, 4.0], [3.0, 6.0]]]

In a more "pythonic" way you can use a single-line command (which might be harder to understand but does the exact same thing):

result = [[[Lon[index], Lat[index]] for index in entry] for entry in list]

edited Jun 12, 2018 at 14:22

answered Jun 12, 2018 at 14:16

Cristian Ramon-Cortes

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1 Comment

Cristian Ramon-Cortes Over a year ago

@mrcbrbr Glad to hear it. Please consider accepting this answer if it was useful.

zipa · Accepted Answer · 2018-06-12 14:16:14Z

1

I'm guessing you need something like this:

[[[Lon[i], Lat[i]] for i in sub] for sub in mylist]
#[[[2.0, 4.0], [1.0, 2.0]],
# [[2.0, 4.0], [2.0, 3.0], [3.0, 1.0]],
# [[3.0, 6.0], [5.0, 5.0], [6.0, 4.0]],
# [[3.0, 6.0], [4.0, 7.0]],
# [[2.0, 4.0], [3.0, 6.0]]]

answered Jun 12, 2018 at 14:16

zipa

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