How does Python insertion sort work?

Question

Here\'s a Python implementation of insertion sort, I tried to follow the values on paper but once the counting variable i gets bigger than len(s) I don\'t know what to do, h

Answer 1

The python range(start, end) function starts counting from start to end - 1. That is, end will never be part of the range() values. So if you have, for example, range(len(A)), and A is an array (in Python, a list) of 10 integers, len(A) will be 10, and range(len(A)) will return (0,1,2,3,4,5,6,7,8,9) so you can index every element in A.

In your case, i never gets bigger than len(s) - 1.

Following your code on paper can be useful, but you have to make sure that the programming language does exactly what you think it does, and sometimes the implementation isn't intuitive. A fast and simple way of tracing your program values is to use print statements. For example:

def sort_numbers(s):
    for i in range(1, len(s)):

        # let's see what values i takes on
        print "i = ", i

        val = s[i]
        j = i - 1
        while (j >= 0) and (s[j] > val):
            s[j+1] = s[j]
            j = j - 1
        s[j+1] = val

Answer 2

__author__ = 'Dharmjit'  
def InsertionSort(list):  
    for index in range(1,len(list)):  
        curr = list[index]  
        position = index  

        while position > 0 and list[position-1] > curr:  
            list[position] = list[position-1]  
            position = position - 1  

        list[position] = curr  
    return list  

l = [2,1,5,3,9,6,7]  
print(InsertionSort(l))  
[1,2,3,5,6,7,9]  

You can see the whole concept here- http://pythonplanet.blogspot.in/2015/07/sorting-algorithm-1-insertion-sort.html

Answer 3

A simple combination of list slicing and bubble sort

s = [54,26,93,17,77,31,44,55,20]

for i in range(1,len(s)+1):
    b = s[0:i]
    a = b
    count = 0

    while count<len(a):                  # while loop to perform the for loop len(a) number of times-like in bubble sort
        for j in range(len(a)-1):        # for loop compares every j'th element with next element
            if a[j] >= a[j+1-len(a)]:
                temp = a[j]
                a[j] = a[j+1-len(a)]
                a[j+1-len(a)] = temp

        count = count+1
print a    

Answer 4

I have looked through a number of these posts and i think that people are over complicating this issue. please correct me if i have done this wrong but this is my interpretation of the sort.

def insert(L): # this creates the definition and assines the list that you input to L
    for i in range(len(L)): # this then loops the next code for the length of the list
        while i > 0 and L[i] < L[i-1]: # this is the main part of the code where it checks
        # if the value from the list is less than the one before it and if it is then it 
        # swaps them around 
            L[i-1], L[i] = L[i], L[i-1] # this code just swaps round the values
            print (L)# prints the list out at the end of each part



L = [5,2,3,7,6,9,7]
insert(L)

Using this it outputs:

[2, 5, 3, 7, 6, 9, 7]
[2, 3, 5, 7, 6, 9, 7]
[2, 3, 5, 6, 7, 9, 7]
[2, 3, 5, 6, 7, 7, 9]

The print function can also be removed from line and can be placed outside the for loop so that it only prints the list at the end. Which would only give the last line:

[2, 3, 5, 6, 7, 7, 9]

Answer 5

+An alternative with two for loops and descriptive names.

def insertionSort(list):
  for outerIndex in range(len(list)):
    for innerIndex in range(outerIndex, 0, -1):
      if list[innerIndex] >= list[innerIndex - 1]:
        break
      list[innerIndex], list[innerIndex - 1] = list[innerIndex - 1], list[innerIndex]
  return list

print insertionSort([3, 1e-10, 7e5, 2.3, 100, -2.5, 12.1])
# => [-2.5, 1e-10, 2.3, 3, 12.1, 100, 700000.0]

Answer 6

    def insertie(x):
    nrc=0
    nrm=0
    for i in range(0,len(x)):
        aux=x[i]
        nrm=nrm+1
        j=i-1
        while j >= 0 and aux < x[j]:
            nrc=nrc+1
            x[j+1]=x[j]
            nrm=nrm+1
            j=j-1
        nrc=nrc+1
        x[j+1]=aux
        nrm=nrm+1
    return x

x=[7,5,4,9,1,4,0,1]
print insertie(x)