How to merge lists to nested list?

Question

I have a list (iris data sample) and i want to scale variables (all but last column). I made a loop to do that, but i can't figure out how to merge them after this process.

X = [[5.1, 3.5, 1.4, 0.2, 0.0],
     [4.9, 3.0, 1.4, 0.2, 0.0],
     [4.7, 3.2, 1.3, 0.2, 0.0],
     [4.6, 3.1, 1.5, 0.2, 0.0],
     [5.0, 3.6, 1.4, 0.2, 0.0],
     [5.4, 3.9, 1.7, 0.4, 0.0]]

I've tried to make a loop to scale but i can't figure out how to merge after.

I tried:

from statistics import mean, stdev
for i in range(len(X)):
    valores = []
    for j in range(len(X[i])-1):
        z = []
        coluna = [item[j] for item in X]
        media = mean(coluna)
        desv = stdev(coluna)
        z = [round(((x - media) / desv), 4) for x in coluna]
        valores = valores + z
valores = valores + [valor[-1] for valor in X]

My actual results are:

valores = [0.5207,-0.1736,-0.8678,-1.2149,0.1736,1.562,0.3401,-1.1175,-0.5345,-0.826,0.6316,1.5062,-0.3627,-0.3627,-1.0882,0.3627,-0.3627,1.8137,-0.4082,-0.4082,-0.4082,-0.4082,-0.4082,2.0412,0.0,0.0,0.0,0.0,0.0,0.0]

But i would like to get:

valores = [[0.5207, 0.3401, -0.3627, -0.4082, 0.0],
           [-0.1736, -1.1175, -0.3627, -0.4082, 0.0],
           [-0.8678, -0.5345, -1.0882, -0.4082, 0.0],
           [-1.2149, -0.826, 0.3627, -0.4082, 0.0],
           [0.1736, 0.6316, -0.3627, -0.4082, 0.0],
           [1.562, 1.5062, 1.8137, 2.0412, 0.0]]

Answer 1

Use pandas:

Data:

X = [[5.1, 3.5, 1.4, 0.2, 0.0],
     [4.9, 3.0, 1.4, 0.2, 0.0],
     [4.7, 3.2, 1.3, 0.2, 0.0],
     [4.6, 3.1, 1.5, 0.2, 0.0],
     [5.0, 3.6, 1.4, 0.2, 0.0],
     [5.4, 3.9, 1.7, 0.4, 0.0]]

Code:

• Write function def valores to produce the required transformation
• Create a dataframe with X
• Apply valores to the appropriate columns in the dataframe

import pandas as pd

def valores(x):
    return [round(((y - x.mean()) / x.std()), 4) for y in x]

df = pd.DataFrame(X)

df[[0, 1, 2, 3]] = df[[0, 1, 2, 3]].apply(lambda x: valores(x))

Output:

      0       1       2       3    4
 0.5207  0.3401 -0.3627 -0.4082  0.0
-0.1736 -1.1175 -0.3627 -0.4082  0.0
-0.8678 -0.5345 -1.0882 -0.4082  0.0
-1.2149 -0.8260  0.3627 -0.4082  0.0
 0.1736  0.6316 -0.3627 -0.4082  0.0
 1.5620  1.5062  1.8137  2.0412  0.0

Answer 2

Not elegant:

out = []
for i in range(1+len(valores)//len(X)):
    aux = []
    for j in range(len(X[0])):
        aux.append(valores[i+len(X)*j])
    out.append(aux)
print(out)

[[0.5207, 0.3401, -0.3627, -0.4082, 0.0], [-0.1736, -1.1175, -0.3627, -0.4082, 0.0], [-0.8678, -0.5345, -1.0882, -0.4082, 0.0], [-1.2149, -0.826, 0.3627, -0.4082, 0.0], [0.1736, 0.6316, -0.3627, -0.4082, 0.0], [1.562, 1.5062, 1.8137, 2.0412, 0.0]]