Increase all elements of a list except the first one in Python-CodePudding

I have a list T1. I want to increase all elements of T1 by 1 except the first element. How do I do so?

T1=[0,1,2,3,4,5,6,7]
T2=[i 1 for i in T1]

The current output is

T2= [1, 2, 3, 4, 5, 6, 7, 8]

The expected output is

T2= [0, 2, 3, 4, 5, 6, 7, 8]

CodePudding user response：

Use slicing!

T1 = [0,1,2,3,4,5,6,7]
T2 = [T1[0]]   [i 1 for i in T1[1:]]

Or, with enumerate:

T1 = [0,1,2,3,4,5,6,7]
T2 = [x (i>0) for i, x in enumerate(T1)]

Output:

[0, 2, 3, 4, 5, 6, 7, 8]

CodePudding user response：

You could separate the first element from the rest and increment the rest by 1 -

first, *rest = t1
t2 = [first]   [(i   1) for i in rest]

Or you could enumerate your list and use the index -

t2 = [(val   1) if idx > 0 else val for (idx, val) in enumerate(t1)]

CodePudding user response：

The correct answer would be to slice the T1 list in two, the part that you don't want to modify and the part that you do. Just combine them afterwards:

T1=[0,1,2,3,4,5,6,7]
T2= T1[0:1]   [i 1 for i in T1[1:]]

CodePudding user response：

There are several methods, 2 of them

T2 = [T1[0]]   [ j 1 for j in T1[1:]]

a longer but funnier one

T2 = [x y for x,y in zip(T1, [0]   [1]*(len(T1)-1))]

or just a for loop with index, so you can decide which index to operate in

T2 = list()
for i,el in enumerate(T1):
    if i == 0:
        T2.append(el)
    else:
        T2.append(el 1)

Have fun

CodePudding user response：

I've tried this:

given:

t1 = [0, 1, 2, 3, 4]

the t2 list may be calculated as following:

t2 = t1[0:1]   [v   1 for i, v in enumerate(t1) if i != 0]

The first part of the list concatenation is a list: in fact if you try t1[0] you get a TypeError due to the fact that is impossible to concatenate int with list.

CodePudding user response：

I would do it like this:

for i in range(1,len(T1)):   
  T1[i]=T1[i] 1

This would not create a new list, but would change the values in the current list

CodePudding user response：

Relatively simple answer where you use if else condition.

T1=[0,1,2,3,4,5,6,7]
T2 = [x 1 if i>0 else x for i, x in enumerate(T1)]

# Output:
[0, 2, 3, 4, 5, 6, 7, 8]