How do you access the 2d list of elements in python?
I have a list of variables in python and I would like to be able to access the index of individual values in each row and column. Because I am new to python, I do not know if there is another way to access the index or select individual values by row and column. Show
The only way I have found so far is to use the pandas library, but I cannot use pandas because of a problem in installation. Please advise me on how to create a dataframe(without using pandas) or any other data structure so that I can access its values by their index, by row and column. Let's say I have the following list: (Actually when I try to find the data structure type, python says it is a list.
Let's say we name it "habits" I would like to access individual values, such as habits[3,2] and I would like to have the result as 80 which is located at the 3rd index of rows and at the 2nd index of columns.
1. Nested lists: processing and printingIn real-world Often tasks have to store rectangular data table. [say more on this!] Such tables are called matrices or two-dimensional arrays. In Python any table can be represented as a list of lists (a list, where each element is in turn a list). For example, here's the program that creates a numerical table with two rows and three columns, and then makes some manipulations with it: a = [[1, 2, 3], [4, 5, 6]] print(a[0]) print(a[1]) b = a[0] print(b) print(a[0][2]) a[0][1] = 7 print(a) print(b) b[2] = 9 print(a[0]) print(b) The first element of To process 2-dimensional array, you typically use nested loops. The first loop iterates through the row number, the second loop runs through the elements inside of a row. For example, that's how you display two-dimensional numerical list on the screen line by line, separating the numbers with spaces: a = [[1, 2, 3, 4], [5, 6], [7, 8, 9]] for i in range(len(a)): for j in range(len(a[i])): print(a[i][j], end=' ') print() We have already tried to explain that a for-loop variable in Python can iterate not only over a a = [[1, 2, 3, 4], [5, 6], [7, 8, 9]] for row in a: for elem in row: print(elem, end=' ') print() Naturally, to output a single line you can use method for row in a: print(' '.join([str(elem) for elem in row])) This is how you can use 2 nested loops to calculate the sum of all the numbers in the 2-dimensional list: a = [[1, 2, 3, 4], [5, 6], [7, 8, 9]] s = 0 for i in range(len(a)): for j in range(len(a[i])): s += a[i][j] print(s) Or the same with iterating by elements, not by the variables
a = [[1, 2, 3, 4], [5, 6], [7, 8, 9]] s = 0 for row in a: for elem in row: s += elem print(s) Advertising by Google, may be based on your interests 2. Nested lists: creatingSuppose that two numbers are given: the number of rows of The obvious solution appears to be wrong: a = [[0] * m] * n This can be easily seen if you set the value of Using our visualizer, keep track of the id of lists. If two lists have the same id number, it's actually the same list in memory. n = 3 m = 4 a = [[0] * m] * n a[0][0] = 5 print(a[1][0]) Thus, a two-dimensional list cannot be created simply by repeating a string. What to do?.. A possible way: you can create a list of
n = 3 m = 4 a = [0] * n for i in range(n): a[i] = [0] * m Another (but similar) way: create an empty list and then n = 3 m = 4 a = [] for i in range(n): a.append([0] * m) But the easiest way
is to use generator, creating a list of n = 3 m = 4 a = [[0] * m for i in range(n)] In this case each element is created independently from the others. The list Advertising by Google, may be based on your interests 3. How do you input a two-dimensional array?Say, a program takes on input two-dimensional array in the form of # the first line of input is the number of rows of the array n = int(input()) a = [] for i in range(n): a.append([int(j) for j in input().split()]) Or, without using sophisticated nested calls: # the first line of input is the number of rows of the array n = int(input()) a = [] for i in range(n): row = input().split() for i in range(len(row)): row[i] = int(row[i]) a.append(row) You can do the same with generators: # the first line of input is the number of rows of the array n = int(input()) a = [[int(j) for j in input().split()] for i in range(n)] Advertising by Google, may be based on your interests 4. Processing a two-dimensional array: an exampleSuppose you are given a square array (an array of 1 0 0 0 2 1 0 0 2 2 1 0 2 2 2 1 (In this case you can do it manually by setting We are eager to show you several ways of solving this problem. First, note that elements that lie above the main diagonal – are elements n = 4 a = [[0] * n for i in range(n)] for i in range(n): for j in range(n): if i < j: a[i][j] = 0 elif i > j: a[i][j] = 2 else: a[i][j] = 1 for row in a: print(' '.join([str(elem) for elem in row])) This algorithm is slow: it uses two loops and for each pair First, fill the main diagonal, for which we will need one loop: for i in range(n): a[i][i] = 1 Then fill with zeros all the elements above the main diagonal. To make this, for each row with the number for i in range(n): for j in range(i + 1, n): a[i][j] = 0 By analogy, for for i in range(n): for j in range(0, i): a[i][j] = 2 You can combine all this code and receive another solution: n = 4 a = [[0] * n for i in range(n)] for i in range(n): for j in range(0, i): a[i][j] = 2 a[i][i] = 1 for j in range(i + 1, n): a[i][j] = 0 for row in a: print(' '.join([str(elem) for elem in row])) Here's another solution, which repeats lists to build the next rows of the list. The n = 4 a = [0] * n for i in range(n): a[i] = [2] * i + [1] + [0] * (n - i - 1) for row in a: print(' '.join([str(elem) for elem in row])) As usual, you can replace the loop with the generator: n = 4 a = [0] * n a = [[2] * i + [1] + [0] * (n - i - 1) for i in range(n)] for row in a: print(' '.join([str(elem) for elem in row])) Advertising by Google, may be based on your interests 5. Two-dimensional arrays: nested generatorsYou can use nested generators to create two-dimensional arrays, placing the generator of the list which is a string, inside the generator of all the strings. Recall that you can create a list of [[0] * m for i in range(n)] But the internal list can also be created using, for example, such generator: [[0 for j in range(m)] for i in range(n)] How is it related to our problem? The thing is, if the number 0 is replaced by some expression that depends on For example, suppose you need to initialize the following array (for convenience, extra spaces are added between items): 0 0 0 0 0 0 0 1 2 3 4 5 0 2 4 6 8 10 0 3 6 9 12 15 0 4 8 12 16 20 In this array there are As always, you could use generator to create such an array: [[i * j for j in range(m)] for i in range(n)] Advertising by Google, may be based on your interests How do you access the elements in a 2D list?Access Two-Dimensional Array
In Python, we can access elements of a two-dimensional array using two indices. The first index refers to the indexing of the list and the second index refers to the position of the elements.
How do you accept a 2D list in Python?Here I have mentioned the basic to take 2d array input:. n_rows= int(input("Number of rows:")). n_columns = int(input("Number of columns:")). #Define the matrix.. matrix = [ ]. print("Enter the entries row-wise:"). #for user input.. for i in range(n_rows): # A for loop for row entries.. a =[ ]. What is 2D list in Python?Two dimensional array is an array within an array. It is an array of arrays. In this type of array the position of an data element is referred by two indices instead of one. So it represents a table with rows an dcolumns of data.
How do I view a 2D array?Example. public class Print2DArray { public static void main(String[] args) { final int[][] matrix = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } }; for (int i = 0; i < matrix. length; i++) { //this equals to the row in our matrix. for (int j = 0; j < matrix[i].
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