Hamood Elholandy - 10 months ago 30

Python Question

I have a 2D array list that contains (x,y), however I want to sort this list by the Equation of Minimum value of (square root of (x^2 + y^2)).

For example I have these four 2D lists:

`(20,10)`

(3,4)

(5,6)

(1.2,7)

If I take the square root of each 2D array in this list and return the minimum of the sorted list, the output is:

`(3,4)`

(1.2,7)

(6.5,4)

(5,6)

(20,10)

the Code :

`M=[ [20,10],[3,4],[5,6],[1.2,7],[6.5,4]]`

s=np.sqrt(M)

a=[]

print s

for i in range(0,h):

`for j in range(0,w):`

a[i] =s[i][j]+a[i]

Any ideas?

Answer

Switch your data structure to a list of tuples and then sort using minimal value as the key function (with memoization for efficiency):

```
M = [(20, 10), (3, 4), (5,6), (1.2, 7), (6.5, 4)]
def minimum_value(coordinate, dictionary={}): # intentional dangerous default value
if coordinate not in dictionary:
dictionary[coordinate] = coordinate[0]**2 + coordinate[1]**2
return dictionary[coordinate]
M_sorted = sorted(M, key=minimum_value)
print(M_sorted)
```

**OUTPUT**

```
[(3, 4), (1.2, 7), (6.5, 4), (5, 6), (20, 10)]
```

Since we're only sorting, we don't need to calculate the square roots, the squares are sufficient.

Source (Stackoverflow)