Filtering array of arrays

Question

I am having this array of arrays containing locations and time information:

my_array[:5]
[['39.921712' '116.472343' '0' '13' '39298.1462037037' '2007-08-04' '03:30:32']
 ['42.161385' '123.660773' '0' '221' '39298.6697337963' '2007-08-04' '16:04:25']
 ['42.161755' '123.66135' '0' '221' '39298.6697569444' '2007-08-04' '16:04:27']
 ['42.16194' '123.661638' '0' '221' '39298.6697685185' '2007-08-04' '16:04:28']
 ['39.907285' '116.448303' '0' '98' '39298.1581134259' '2007-08-04' '03:47:41']]

The first and second elements of each array are the position´s latitude and longitude.

I want to filter my_array to contain only those arrays where the latitude falls between 39.45 - 40.05 and the longitude fall between 115.416 - 117.5.

Expected out:

my_array_sorted
[['39.921712' '116.472343' '0' '13' '39298.1462037037' '2007-08-04' '03:30:32']
 ['39.907285' '116.448303' '0' '98' '39298.1581134259' '2007-08-04' '03:47:41']]

Have you tried code? Are there any errors?

7u5h4r
– 7u5h4r

2020-06-24 21:18:13 +00:00
Commented Jun 24, 2020 at 21:18 — 7u5h4r
– 7u5h4r, Commented Jun 24, 2020 at 21:18
Are these numpy arrays or python lists?

Barmar
– Barmar

2020-06-24 21:21:51 +00:00
Commented Jun 24, 2020 at 21:21 — Barmar
– Barmar, Commented Jun 24, 2020 at 21:21

bherbruck · Accepted Answer · 2020-06-24 21:23:45Z

2

You can do this with a list comprehension:

data = [['39.921712', '116.472343', '0', '13', '39298.1462037037', '2007-08-04', '03:30:32'],
 ['42.161385', '123.660773', '0', '221', '39298.6697337963', '2007-08-04', '16:04:25'],
 ['42.161755', '123.66135', '0', '221', '39298.6697569444', '2007-08-04', '16:04:27'],
 ['42.16194', '123.661638', '0', '221', '39298.6697685185', '2007-08-04', '16:04:28'],
 ['39.907285', '116.448303', '0', '98', '39298.1581134259', '2007-08-04', '03:47:41'],]

filtered = [i for i in data
            if 39.45 < float(i[0]) < 40.05
            and 115.416 < float(i[1]) < 117.5]

print(filtered)

Output:

[['39.921712', '116.472343', '0', '13', '39298.1462037037', '2007-08-04', '03:30:32'],
['39.907285', '116.448303', '0', '98', '39298.1581134259', '2007-08-04', '03:47:41']]

answered Jun 24, 2020 at 21:23

bherbruck

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Noé Mastrorillo · Accepted Answer · 2020-06-24 21:18:11Z

1

You should look at python's filter method that takes a predicate and your list, and keep only the elements that complete the predicate.

Here is an example taken from the documentation above:

number_list = range(-5, 5)
less_than_zero = list(filter(lambda x: x < 0, number_list))
print(less_than_zero)

# Output: [-5, -4, -3, -2, -1]

In your case it should looks like this:

my_array_sorted = list(filter(lambda array: 39.45 < array[0] < 40.05 and 115.416 < array[1] < 117.5))

answered Jun 24, 2020 at 21:18

Noé Mastrorillo

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2 Comments

bherbruck Over a year ago

interesting thing another user on SO showed me about a lot of the built-in python functions like filter, map, etc. is that comprehensions are in many cases a little faster, also more "pythonic", and a bit easier to read

Noé Mastrorillo Over a year ago

@TenaciousB callbacks are a bit hard to understand when you are new to python. I'm personnaly used to use lambdas as I come from Java where we have Consumer, Predicate, etc. But basically both approaches work and it's just a matter of taste.

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