Python通过跳过列表之间的值将值追加到空列表

Question

Just a minimal example of what I want to achieve.

I have an array:

array = [1,2,3,4,5,6,7,8,9,10,1,2,3,4,5,6,7,8,9,10,....,1,2,3,4,5,6,7,8,9,10]

I would like to loop through this array and create a new array which looks like this:

new_array = [1,1,2,1,2,3,1,2,3,4,1,2,3,4,5,....,1,2,3,4,5,6,7,8,9,10]

ie loop through array a , get the first value (ie 1), then skip the remaining 9 values , then get the first and the second value (ie 1,2), then skip the remaining 8 values , and so on.

The idea I came up with was to create indices and use it in the following way:

In [1]: indices = np.arange(1,10,1)
Out[1]: array([1, 2, 3, 4, 5, 6, 7, 8, 9])

new_array = []
for i in array:
    for a,b in zip(indices,range(10)):
        new_array.append(i[0:a]) # here I am including i[0:1], i[0:2] and so on 

So it loops through array and gets the first value, then skips the remaining 9 values, then gets the first two values and skips the remaining 8 values and so on.

But this doesn't seem to work. How can I achieve this ?

Answer 1

If you don't need all values (only pass your scheme)

list = [1,2,3,4,5,6,7,8,9,10] * 10
output = []

skip = 9
i = 0
while skip > 0:
    output.append(list[i])
    i += skip + 1
    skip -= 1
print(list)
print(output)

But your "new_array" doesn't pass your algorithm. Why not:

[1,2,3,4,5,6,7,8,9,10,1,2,3,4,5,6,7,8,9,10,1,2,3,4,5,6,7,8,9,10] If I get first 1 (it has index 0 ) after skip 9 values I will get 1 , after then skipping 8 values I won't get 2

Edit: Ok, I understand now. This should work:

list = [1,2,3,4,5,6,7,8,9,10] * 10
output = []

skip = 9
i = 0
j = 0
add = 1
while skip >= 0:
    newList = list[i:j+1]
    for x in newList:
        output.append(x)
    i += skip + add
    j += skip + add + 1
    add += 1
    skip -= 1
print(output)

Answer 2

can you please try this code. I have tested this code on python 3 and it is working fine.

inp = [1,2,3,4,5,6,7,8,9,10] * 10
inp_len = len(inp);
output = [inp[0]]
skip = 9
limit= skip +2;
pointer = 1;
while skip > 0:
    pointer = pointer+skip;
    if(pointer >inp_len):
        pointer = pointer %inp_len;
    for x in inp[pointer : pointer+limit-skip ]:
        output.append(x);
    pointer= pointer+ limit-skip ;
    skip=skip-1;
print(inp)
print(output)

Explaination - Adding default first element and then adding elements in below order.

• skip 9 elements = [1, 2]
• skip 8 elements = [1, 2, 3]
• skip 7 elements = [1, 2, 3, 4]
• skip 6 elements = [1, 2, 3, 4, 5]
• skip 5 elements = [1, 2, 3, 4, 5, 6]
• skip 4 elements = [1, 2, 3, 4, 5, 6, 7]
• skip 3 elements = [1, 2, 3, 4, 5, 6, 7, 8]
• skip 2 elements = [1, 2, 3, 4, 5, 6, 7, 8, 9]
• skip 1 elements = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Please test it with your input . Here i am using a defined list.

Input list -[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Output list - [1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 7, 1, 2, 3, 4, 5, 6, 7, 8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Answer 3

For a signle list you can also use list extension for this:

list = [1,2,3,4,5,6,7,8,9,10]
output = []
i = 1
while i <= 10:
    output.extend(list[0:i])
    i +=1

print output

For your list you can extend this to:

list = [1,2,3,4,5,6,7,8,9,10]*10

output = []

i = 1
j = 0
k = 1
while k <= 10:
   output.extend(list[j:i])
   j +=10
   k +=1
   i = j+k

print output   

Answer 4

How about:

list = [1,2,3,4,5,6,7,8,9,10] * 10;
output = [];

take = 1;
index = 0;
while index < len(list):
    # take the "take" next elements, notice the "index" is not changing.
    for i in range(take):
        output.append(list[index + i]);
    # Skip the remaining values and increase the "take"
    index += 10;
    take += 1;
print(list)
print(output)

You can also go like this with two indices:

list = [1,2,3,4,5,6,7,8,9,10] * 10;
output = [];

index = 0;
for i in range(10):
    for j in range(10):
        if j <= i:
            output.append(list[index + i]);
        index++;
print(list)
print(output)

Answer 5

it's not too different from printing a triangle with numbers from 1 to 10.

array     = [x for x in range(1,11)]*10 #here 10 means adding same list 10 times
new_array = []
for i in range(10):
    new_array += array[10*i:10*i+i+1]
print(new_array)

hope this helps!

It takes 0.0005 sec

Answer 6

array = [1,2,3,4,5,6,7,8,9,10]*10
new_array = []

c=j=0
while c < len(array):
    for i in range(0,j):
        new_array.append(array[i])
        i+=1
    j+=1
    c+=10
print(new_array)

Output

[1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 7, 1, 2, 3, 4, 5, 6, 7, 8, 1, 2, 3, 4, 5, 6, 7, 8, 9]