Chichi - 5 months ago 22

Python Question

I have this data structure:

It is 2d-array that is divided on **3** sections. For each letter in the array I need to define **Section** number. For example, letters

`a,b,c,d`

`e,f,g,h`

My code. Firstly, this 2d-array preparation:

`from itertools import cycle`

letters = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l']

#2d-array initialization

width, height = 3, 6

repRange = cycle(range(1, 3))

values = [0] * (width - 1)

array2d = [[next(repRange)] + values for y in range(height)]

#Filling array with letters:

m = 0

for i in range(height):

for j in range(1,width):

array2d[i][j] = letters[m]

m+=1

#Printing:

for row in array2d:

print(row)

`[1, 'a', 'b']`

[2, 'c', 'd']

[1, 'e', 'f']

[2, 'g', 'h']

[1, 'i', 'j']

[2, 'k', 'l']

Now I need to determine section number of each letter and save it along with the letter itself. I use

`defineSection`

`def defineSection(i, division, height):`

if i <= division:

return 1

elif division*2 >= i > division :

return 2

elif division*3 >= i > division*2 :

return 3

dic = {}

for i in range(height):

for j in range(1,width):

section = defineSection(i+1, 2, height)

dic.update({array2d[i][j] : section})

for item in dic.items():

print(item)

`('f', 2)`

('b', 1)

('c', 1)

('e', 2)

('k', 3)

('g', 2)

('d', 1)

('a', 1)

('l', 3)

('h', 2)

('i', 3)

('j', 3)

It defined all section numbers for each letter correctly. But

`defineSection`

I don't know how to implement

`defineSection`

`if-elif`

Answer

You can simplify your matrix creation code immensely. All you need is a `letters`

iterator, which returns itself so you can iterate 2-letters at a time using zip.

```
In [3]: from itertools import cycle
In [4]: letters = "abcdefghijkl"
In [5]: ranges = cycle(range(1,3))
In [6]: iter_letters = iter(letters)
In [7]: matrix = [[i,a,b] for i,a,b in zip(ranges,iter_letters,iter_letters)]
In [8]: matrix
Out[8]:
[[1, 'a', 'b'],
[2, 'c', 'd'],
[1, 'e', 'f'],
[2, 'g', 'h'],
[1, 'i', 'j'],
[2, 'k', 'l']]
```

As for assigning sections, note that a section is every two rows, which is *four* letters, so you can use simple floor division to "skip" counts.

```
In [9]: sections = {letter:(i//4 + 1) for i,letter in enumerate(letters)}
In [10]: sections
Out[10]:
{'a': 1,
'b': 1,
'c': 1,
'd': 1,
'e': 2,
'f': 2,
'g': 2,
'h': 2,
'i': 3,
'j': 3,
'k': 3,
'l': 3}
```