CODEWITHSUNDEEP
python
riyalaise123
riyalaise123

Reputation: 43

Inserting Value into a List with designated position

I'm attempting to make a function that when called, takes a list, value, and insert position, and returns a copy of the list with the value inserted at the place specified by the insert position. For this task (due to request), I'm unable to use bulit in functions (other than range(), slice expressions, list methods (apart from append()) or string methods. Any help would be greatly appreciated 

def insert_value(my_list, value, insert_position):

 new_list = []
 for i in my_list:
     new_list.append(i)

 if insert_position > length(my_list):
     new_list.append(value)
     return new_list
 elif insert_position <= 0:
     new_list.append(value[0])
     return new_list

str_list3 = ['one','three','four', 'five', 'six']
new_list = list_function.insert_value(str_list3, 'two', 1)
print(new_list)

Upvotes: 0

Views: 1626

Answers (4)

Sraw
Sraw

Reputation: 20216

Update

A more understandable one

def insert_value(my_list, value, insert_position):
    new_list = []
    if insert_position <= 0:
        new_list.append(value)
        for i in my_list:
            new_list.append(i)
    elif insert_position >= len(my_list):
        for i in my_list:
            new_list.append(i)
        new_list.append(value)
    else:
        new_list = [None] * (len(my_list) + 1)
        # replace : index = [i for i in range(len(new_list)) if i != insert_position]
        index = []
        for i in range(len(new_list)):
            if i != insert_position:
                index.append(i)
        # end
        new_list[insert_position] = value
        for i in index:
            # replace : new_list[i] = my_list[i if i < insert_position else i - 1]
            if i < insert_position:
                new_list[i] = my_list[i]
            else:
                new_list[i] = my_list[i - 1]
            # end
    return new_list

def insert_value(my_list, value, insert_position):
    new_list = []
    if insert_position <= 0:
        new_list.append(value)
        for i in my_list:
            new_list.append(i)
    elif insert_position >= len(my_list):
        for i in my_list:
            new_list.append(i)
        new_list.append(value)
    else:
        new_list = [None] * (len(my_list) + 1)
        index = [i for i in range(len(new_list)) if i != insert_position]
        new_list[insert_position] = value
        for i in index:
            new_list[i] = my_list[i if i < insert_position else i - 1]
    return new_list

Upvotes: 1

Chris
Chris

Reputation: 22953

This can be accomplished very simply using slice notation.

You known what your function needs to do. Insert a given value into a given position in a given list. Basically, you need to split the list into two parts. The first part contains all the elements before the given index. The second part contains all the elements after the given index. Once you have those two parts, you can simply "sandwich" the given value in between.

Here is visual demonstrating what I mean. Assume the index is equal to 1:

  first part      value             second part
     |              |                    |
    [1]-------------2----------------[3][4][5]
     |                                   |
     |                                   |
     |                                   |
     + all elements *before* index 1     + all elements *after* index 1

Here is how the implementation would look like:

>>> def insert_value(lst, value, idx):
...     # elements before idx
...     front = lst[:idx]
...     # elements after idx
...     back = lst[idx:]
...     # "sandwhiching" the value between the front and back parts
...     return front + [value] + back

example:

>>> lst = [1, 3, 4, 5]
>>> insert_value(lst, 2, 1)
[1, 2, 3, 4, 5]
>>>

I'm not exactly sure if you have to, but it would be trivial to implement a check to see if the given index is in the bounds of the lists.

Upvotes: 2

Prashant Bhardwaj
Prashant Bhardwaj

Reputation: 86

do this : 

def insert_value(my_list, value, insert_position):
new_list = []
for i in range(0, len(my_list)+1):
    if i < insert_position:
        new_list.append(my_list[i])
    elif insert_position == i:
        new_list.append(value)
    else:
        new_list.append(my_list[i-1])
return new_list
str_list3 = ['one','three','four', 'five', 'six']
new_list = insert_value(str_list3, 'two', 1)
print(new_list)

Upvotes: 0

Pavan
Pavan

Reputation: 108

You can do this, given that you're inserting a single value:

def insert_value(my_list, value, insert_position):
    new_list = []
    for i in range(0, insert_position)
        new_list.append(my_list[i])
    new_list.append(value)
    for i in range(insert_position, len(my_list)+1)
        new_list.append(my_list[i-1])

If you can use splicing and append, then

def insert_value(my_list, value, insert_position):
    new_list = my_list[:insert_position]
    new_list.append(value)
    new_list = new_list+my_list[insert_position:]

Upvotes: 0

Related Questions