Converting Two Lists into a Matrix

Converting two lists into a matrix

The standard numpy function for what you want is np.column_stack:

>>> np.column_stack(([1, 2, 3], [4, 5, 6]))
array([[1, 4],
       [2, 5],
       [3, 6]])

So with your portfolio and index arrays, doing

np.column_stack((portfolio, index))

would yield something like:

[[portfolio_value1, index_value1],
 [portfolio_value2, index_value2],
 [portfolio_value3, index_value3],
 ...]

Python: how to combine two flat lists into a 2D array?

list(zip(lat, long))

gives

[(48.01, -6.15), (48.02, -6.1), (48.03, -6.05), (48.04, -6.0), 
 (48.05, -5.95), (48.06, -5.9), (48.07, -5.85), (48.08, -5.79), (48.1, -5.74)]

More on zip here

Converting a list of lists into a 2D numpy array

If your lists are NOT of the same length (in each nested dimension) you CANT do a traditional conversion to a NumPy array because it's necessary for a NumPy array of 2D or above to have the same number of elements in its first dimension.

So you cant convert [[1,2],[3,4,5]] to a numpy array directly. Applying np.array will give you a 2 element numpy array where each element is a list object as - array([list([1, 2]), list([3, 4, 5])], dtype=object). I believe this is the issue you are facing.

You cant create a 2D matrix for example that looks like -

[[1,2,3,?],
 [4,5,6,7]]

What you may need to do is pad the elements of each list of lists of lists to a fixed length (equal lengths for each dimension) before converting to a NumPy array.

I would recommend iterating over each of the lists of lists of lists as done in the code I have written below to flatten your data, then transforming it the way you want.

---

If your lists are of the same length, then should not be a problem with numpy version 1.18.5 or above.

a = [[[1,2],[3,4]],[[5,6],[7,8]]]
np.array(a)

array([[[1, 2],
        [3, 4]],

       [[5, 6],
        [7, 8]]])

However, if you are unable to still work with the list of list of lists, then you may need to iterate over each element first to flatten the list and then change it into a numpy array with the required shape as below -

a = [[[1,2],[3,4]],[[5,6],[7,8]]]
flat_a = [item for sublist in a for subsublist in sublist for item in subsublist]
np.array(flat_a).reshape(2,2,2)

array([[[1, 2],
        [3, 4]],

       [[5, 6],
        [7, 8]]])

Concatenate two lists elementwise to an n x n matrix

Regular Python - using string concatenation and list comprehension:

matrix = [[x + y for x in row] for y in col]

To be compliant with NumPy styling and the desired output use:

np.c_[matrix].T

convert list of lists into matrices

You can use sapply like:

alpha_out <- t(sapply(theta, function(x) {x$alpha}))
alpha_out <- t(sapply(theta, `[[`, 1))

Convert multiple list variables in to a matrix of desired arrangement

mylist <- list(m1, m2, m3)

#make all vectors the same length
mylist <- lapply(mylist, "length<-", max(lengths(mylist)))

#last observation carried forward
library(zoo)
mylist <- lapply(mylist, na.locf)

#rbind
m <- do.call(rbind, mylist)
#     [,1] [,2] [,3]
#[1,] "10" "12" "13"
#[2,] "5"  "6"  "6" 
#[3,] "4"  "4"  "4" 

Print list of lists into matrix format

Try this:

import numpy as np
import pandas as pd

lst = [['1', 'A'],['1', 'B'],['2', 'A'],['2', 'B'],['3', 'A'],['3', 'B']]

def show(lst):
    df = pd.DataFrame(lst, columns=['number', 'letter'])
    a = []
    for x in df['letter'].unique():
        a.append(np.array(df[df['letter']==x]))
    a = np.array(a)
    for i in range(a.shape[1]):
        p = ' '.join([str(list(a[j,i])) for j in range(a.shape[0])])
        print(p)

show(lst)

Output:

['1', 'A']['1', 'B']
['2', 'A']['2', 'B']
['3', 'A']['3', 'B']

If you have more letters and more rows, then this function will still work.

lst = [['1', 'A'],['1', 'B'],['1', 'C'],['1', 'D'],['1', 'E'],['2', 'A'],['2', 'B'],['2', 'C'],['2', 'D'],['2','E'],['3', 'A'],['3', 'B'],['3', 'C'],['3', 'D'], ['3', 'E'],['4', 'A'],['4', 'B'],['4', 'C'],['4', 'D'], ['4', 'E']]

show(lst)

Output:

['1', 'A'] ['1', 'B'] ['1', 'C'] ['1', 'D'] ['1', 'E']
['2', 'A'] ['2', 'B'] ['2', 'C'] ['2', 'D'] ['2', 'E']
['3', 'A'] ['3', 'B'] ['3', 'C'] ['3', 'D'] ['3', 'E']
['4', 'A'] ['4', 'B'] ['4', 'C'] ['4', 'D'] ['4', 'E']

converting list into a matrix in Python

Maybe what you want is a dict:

matrix = {
    k: {l: 0 for l in res}
    for k in res
}

All the values are initialized to 0.

You can easily update values in matrix; for example, you can increase the value of a 'cell' of one:

matrix['(18,430)']['(19,430)'] += 1

or set it to a specific value:

matrix['(18,430)']['(19,430)'] = 10

and retrieve it:

val = matrix['(18,430)']['(19,430)']

---

Related Topics