1. 1D Arrays and Lots of BracketsPs
Module 7 – Part I
1D Arrays and Lots of Brackets
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CSE 1321 Module 7

2. 2. Creating and Initializing Arrays
You must choose: 1) Create an empty arrays and assign initial values with a loop later on: CREATE myArray[5] OR 2) Create and initialize the array in one line. This is helpful when we already know those value (e.g. days of the week, etc.).
4/6/2019
CSE 1321

3. Array Creation Example
We create arrays in Python by first importing the array module.
from array import *
Creation is different. Must include the typecode (‘i’ in the line below).
myArray = array('i',[10, 20, 30, 40, 50]) Typecode Value
b Represents signed integer of size 1 byte/td>
B Represents unsigned integer of size 1 byte
c Represents character of size 1 byte
i Represents signed integer of size 2 bytes
I Represents unsigned integer of size 2 bytes
f Represents floating point of size 4 bytes
d Represents floating point of size 8 byte
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CSE 1321

4. 3. Accessing Information
Copy information out of a particular slot
Example:
CREATE clientAge // Integer
clientAge ← myArray[4]
This copies information from the fifth slot (slot four) into the variable clientAge
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CSE 1321

5. Horrible, but works…
// creates empty array with 5 slots, 0-4 CREATE myArray [5] //Assigns literal values to each index in the array. myArray[0] ← 10 myArray[1] ← 20 myArray[2] ← 30 myArray[3] ← 40 myArray[4] ← 50 Ps
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CSE 1321

6. Accessing and Modifying
#Accessing secondNumber = myArray[1] print(secondNumber)
#Modifying
myArray[3] = 42
print(myArray[3])
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CSE 1321 Module 4

7. Ps Traversing the Array
You will use a loop to visit every cell of the array
Problem: create an array of 5 bytes and fill each slot with the number 42
Solution:
CREATE myArray [5]
FOR i ← 0 to 4
myArray[i] ← 42
END FOR Ps
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CSE 1321

8. Python – Traversing an Array
for x in myArray: #do something. Assignment IS allowed! x = x+10 print(x)
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CSE 1321

9. Another Array Example
from array import * size = 5 myArray = array('i',[0] * size) # All zeroes for x in myArray: print(x) # To fill with 10, 20, 30, 40 and for x in range(len(myArray)): myArray[x] = (x + 1) * 10
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CSE 1321

10. Ps Another Trace CREATE smallestSoFar smallestSoFar ← randomArray[0]
FOR counter ← 1 to 4
IF (smallestSoFar > randomArray[counter]) THEN
smallestSoFar ← randomArray[counter]
END IF
END FOR
// Done
counter 5 1 2 3 4
smallestSoFar -8 42 17 42 -8 4

11. Finding the Minimum using a Function
def function(*args):
temp = myArray[0]
for x in myArray:
if (x < temp):
temp = x
print(temp)
NOTE: Python is different. In Python, Object references are passed by value.
A function receives a reference to (and will access) the same object in memory as used by the caller. However, it does not receive the box that the caller is storing this object in; as in pass-by-value, the function provides its own box and creates a new variable for itself.
4/6/2019
CSE 1321

12. Finding the sum or average using a method
METHOD FINDAVERAGE ( parameter: nums[]) BEGIN sum ← 0 FOR i ← 0 to nums.length - 1 // MOST IMPORTANT LINE IS HERE sum = sum + nums[i] ENDFOR average = sum / nums.length return average END FINDAVERAGE Ps
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CSE 1321

13. Finding a sum and or average using a method
def function(*args):
temp = 0
for x in myArray:
temp = temp + x
print("Average:", temp/len(myArray))
print("Sum: ", temp)
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CSE 1321

14. Ps Defining a 2D array CREATE array nums [numRows][numColumns]
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CSE 1321

15. Python – Define a 2D Array
In Python, 2D Arrays must be initialized when they are created. numbers = [[1,2,3,4,5], [6,7,8,9,10], [11,12,13,14,15], [16,17,18,19,20]]
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CSE 1321

16. Working with 2D arrays
Usually involves nested loops, as shown below Problem Statement: Create an array of 4 rows and 5 columns. Populate the array with the numbers 1-20.
Create array grid[4][5] count ← 1
FOR each element in a row
FOR each element in a column     grid[row][col] = count
count ← count + 1
END INNER FOR END FOR
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CSE 1321

17. Working with 2D arrays from array import *
numbers = [[1,2,3,4,5], [6,7,8,9,10], [11,12,13,14,15], [16,17,18,19,20]]
for r in numbers:
for c in r:
print(c, end = " ")
print()
#what value does this line print?
print(numbers[3][4])
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CSE 1321

18. Python - Working with Lists
colors = list()
#add colors
colors.append('purple')
colors.append('pink')
colors.append('green')
#find if list contains an element
if('pink' in colors):
print('pink is in the list')
print('\n')
#show the index of pink
print(colors.index('pink'))
#remove a color
colors.remove('green')
#output list
for x in range(len(colors)):
print (colors[x])
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CSE 1321