How do I replace all occurrences of an item in a 2D list array

Question

I have this python list array:

yards = [['85', '110', '90', '130', '115', '105', '95', '87', '85'], ['-', '90', '-', '-', '-', '-', '-', '-', '-'], ['-', '-', '-', '-', '-', '-', '-', '-', '-'], ['-', '-', '-', '-', '-', '-', '-', '-', '-']]

but I want to replace all '-' with a zero (0).

yards = [[85, 110, 90, 130, 115, 105, 95, 87, 85], [0, 90, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0]]

This code below is not working as it should because it's not looping all elements only the one defined as yards[1]. How do make it so that any size of 2D list array with element ('-') gets changed to a zero?

print(len(yards))
numeric_types = [str]
yards = [x for x in yards[1] if type(x) in numeric_types]  

print(yards)

for i in range(len(yards)):
  if yards[i] == '-':
      yards[i] = 0

 print(yards) # output of the changed list


4
['-', '90', '-', '-', '-', '-', '-', '-', '-']
[0, '90', 0, 0, 0, 0, 0, 0, 0]

Answer 1

Convert to numpy:

import numpy as np

yards = [['85', '110', '90', '130', '115', '105', '95', '87', '85'], ['-', '90', '-', '-', '-', '-', '-', '-', '-'], ['-', '-', '-', '-', '-', '-', '-', '-', '-'], ['-', '-', '-', '-', '-', '-', '-', '-', '-']]
arr = np.array(yards)

Then to set all the occurrences of '-' to 0, do the following:

arr[arr == '-'] = 0

Answer 2

for l in range(len(yards)):
  for i in range(len(l)):
    if l[i] == '-':
      yards[l][i] = 0

This loops through each sub list and finds the '-' and changes it's value to 0.

Answer 3

if you're already using numpy for something, this is a very easy one-liner:

x = np.array(yards)    
np.where(x=='-',0,x).tolist()

output:

[['85', '110', '90', '130', '115', '105', '95', '87', '85'], ['0', '90', '0', '0', '0', '0', '0', '0', '0'], ['0', '0', '0', '0', '0', '0', '0', '0', '0'], ['0', '0', '0', '0', '0', '0', '0', '0', '0']]

you could also use numpy to typecast the array to ints, floats, etc. if you wanted once the -'s are replaced with numbers

Answer 4

Hendy's answer would output this error:

TypeError: object of type 'int' has no len()

here's how to fix this:

for l in range(len(yards)):
   for i in range(len(yards[l])):
     if yards[l][i] == '-':
       yards[l][i] = 0

Answer 5

You can use nested list comprehensions to convert '-' to 0 (and convert other elements to integers):

[ [0 if r == '-' else int(r) for r in row] 
  for row in yards
]

[[85, 110, 90, 130, 115, 105, 95, 87, 85],
 [0, 90, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0, 0]]

Answer 6

You can iterate through the the 2d list:

for x in range(len(yards)):
     for y in range(len(yards[x])):
         if yards[x][y] == '-':
             yards[x][y] = 0