How do I write a function that replaces all negative numbers in an array with a 0.
Here is what I have so far:
def negativesToZero(A):
for x in A:
if x < 0:
A.append(0)
else:
pass
print A
A = ([[1,-2],\
[-2,1]])
negativesToZero(A)
Since A is a list of lists:
>>> A = [[1, -2], [-2, 1]]
>>> for lst in A:
... for i, val in enumerate(lst):
... lst[i] = max(val, 0)
>>> print A
[[1, 0], [0, 1]]
Alternatively using list comprehensions:
>>> A = [[max(val, 0) for val in lst] for lst in A]
If you want an array operation, you should create a proper array to start with.
A=array([[1,-2],[-2,1]])
Array comprehensions like yours can be one-lined using boolean operations on indices:
A[A<0]=0
Of course you can frame it as a function:
def positive_attitude(x):
x[x<0]=0
return x
print positive_attitude(A)
Go through each sublist in the list. For each sublist, create a new one that turns any negative items into 0. The tidiest way is with a comprehension:
A = [[1,-2], [-2,1]]
A = [[item if item >= 0 else 0 for item in l] for l in A]
Result:
[[1, 0], [0, 1]]
Here is a recursive implementation that will work with any type of list, with any type of input in it:
def convertToZero(arr):
for i in range(len(arr)):
if type(arr[i]) == int and arr[i] < 0:
arr[i] = 0
elif type(arr[i]) == list:
convertToZero(arr[i])
return arr
result = convertToZero( [[1,-2], ['hello',[-2,1]], [-1,'world']] )
print result
# [[1, 0], ['hello', [0, 1]], [0, 'world']]
Here is a simple and easy to understand answer along the lines of what you were trying to do in the beginning:
def negativesToZero(A):
index = 0 #Track your index
for x in A:
if isinstance(x, list): #Calling the program recursively on nested lists
A[index] = negativesToZero(x)
elif x < 0:
A[index] = 0 #Makes negatives 0
else:
pass #Ignores zeros and positives
index += 1 #Move on to next index
print A
return A
If you don't want the unwanted inner print statements you can add an input variable (I will call it 'recur') to the function that makes only the non recursive call print:
def negativesToZero(A, recur = False):
index = 0
for x in A:
if isinstance(x, list):
A[index] = negativesToZero(x, True)
elif x < 0:
A[index] = 0
else:
pass
index += 1
if recur == False: print A
return A
Result:
A = ([[1,-2],\
[-2,1],\
[-5, -6], [4,7]])
negativesToZero(A)
>>>> [[1, 0], [0, 1], [0, 0], [4, 7]]
import numpy as np
listOnums = np.random.normal(size = 300)
listOnums = listOnums.reshape(3,10,10)
def negToZero(arrayOnums):
'''
Takes an array of numbers, replaces values less than 0 with 0
and retuns an array of numbers.
'''
dims = arrayOnums.shape
flatNums = arrayOnums.flatten()
for num,x in enumerate(flatNums):
if x >= 0: pass
else:
flatNums[num] = 0
arrayOnums = flatNums.reshape(dims)
return arrayOnums
negToZero(listOnums)
