I need to figure out how I can find all the index of a value in a 2d numpy array.
For example, I have the following 2d array:
[[[1 1 0 0],
[0 0 1 1],
[0 0 0 0]]]
I need to find the index of all the 1's and 0's.
1: [[0, 0], [0, 1], [1, 2], [1, 3]]
0: [[0, 2], [0, 3], [1, 0], [1, 1], [the entire all row]]
I tried this but it doesn't give me all the indexes:
t = [[index, row.index[1]] for index, row in enumerate[x] if 1 in row]
Basically, it gives me only one of the index in each row [[0, 0], [1, 2]].
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.
In the below example of a two dimensional array, observer that each array element itself is also an array.
Consider the example of recording temperatures 4 times a day, every day. Some times the recording instrument may be faulty and we fail to record data. Such data for 4 days can be presented as a two dimensional array as below.
Day 1 - 11 12 5 2 Day 2 - 15 6 10 Day 3 - 10 8 12 5 Day 4 - 12 15 8 6
The above data can be represented as a two dimensional array as below.
T = [[11, 12, 5, 2], [15, 6,10], [10, 8, 12, 5], [12,15,8,6]]
Accessing Values
The data elements in two dimesnional arrays can be accessed using two indices. One index referring to the main or parent array and another index referring to the position of the data element in the inner array.If we mention only one index then the entire inner array is printed for that index position.
Example
The example below illustrates how it works.
from array import * T = [[11, 12, 5, 2], [15, 6,10], [10, 8, 12, 5], [12,15,8,6]] print[T[0]] print[T[1][2]]
Output
When the above code is executed, it produces the following result −
[11, 12, 5, 2] 10
To print out the entire two dimensional array we can use python for loop as shown below. We use end of line to print out the values in different rows.
Example
from array import *
T = [[11, 12, 5, 2], [15, 6,10], [10, 8, 12, 5], [12,15,8,6]]
for r in T:
for c in r:
print[c,end = " "]
print[]
Output
When the above code is executed, it produces the following result −
11 12 5 2 15 6 10 10 8 12 5 12 15 8 6
Inserting Values
We can insert new data elements at specific position by using the insert[] method and specifying the index.
Example
In the below example a new data element is inserted at index position 2.
from array import *
T = [[11, 12, 5, 2], [15, 6,10], [10, 8, 12, 5], [12,15,8,6]]
T.insert[2, [0,5,11,13,6]]
for r in T:
for c in r:
print[c,end = " "]
print[]
Output
When the above code is executed, it produces the following result −
11 12 5 2 15 6 10 0 5 11 13 6 10 8 12 5 12 15 8 6
Updating Values
We can update the entire inner array or some specific data elements of the inner array by reassigning the values using the array index.
Example
from array import *
T = [[11, 12, 5, 2], [15, 6,10], [10, 8, 12, 5], [12,15,8,6]]
T[2] = [11,9]
T[0][3] = 7
for r in T:
for c in r:
print[c,end = " "]
print[]
Output
When the above code is executed, it produces the following result −
11 12 5 7 15 6 10 11 9 12 15 8 6
Deleting the Values
We can delete the entire inner array or some specific data elements of the inner array by reassigning the values using the del[] method with index. But in case you need to remove specific data elements in one of the inner arrays, then use the update process described above.
Example
from array import *
T = [[11, 12, 5, 2], [15, 6,10], [10, 8, 12, 5], [12,15,8,6]]
del T[3]
for r in T:
for c in r:
print[c,end = " "]
print[]
Output
When the above code is executed, it produces the following result −
11 12 5 2 15 6 10 10 8 12 5
Array is a data structure used to store elements. An array can only store similar types of elements. A Two Dimensional is defined as an Array inside the Array. The index of the array starts with 0 and ends with a size of array minus 1. We can create ‘n’ number of arrays in an array.
In the above image, we can see that an index uniquely identifies each array element.
In this Python List tutorial, you will learn:
- How to Create Array in Python?
- Accessing the values
- Inserting the values into the two-dimensional array
- Updating the values into the two-dimensional array
- Deleting the values from two-dimensional array
- Get the size of two-dimensional array
How to Create Array in Python?
We can create a two-dimensional array[list] with rows and columns.
Syntax:
[[r1,r2,r3,..,rn],[c1,c2,c3,.......,cn]]
Where,
r stands for rows and c stands for columns
Example: Following is the example for creating
2D array with 4 rows and 5 columns
array=[[23,45,43,23,45],[45,67,54,32,45],[89,90,87,65,44],[23,45,67,32,10]] #display print[array]
Output:
[[23, 45, 43, 23, 45], [45, 67, 54, 32, 45], [89, 90, 87, 65, 44], [23, 45, 67, 32, 10]]
Accessing the values
We can access the values using index position
Syntax:
We can get row value using [] operator
array[row index]
We can get column value using [][]
Array[row index][column index]
where,
- array is an input array
- row index is the row index position starts from 0
- column index is the column index position starts from 0 in a row.
Example:
In this example we are going to access the values using index positions
#creare 2D array with 4 rows and 5 columns array=[[23,45,43,23,45],[45,67,54,32,45],[89,90,87,65,44],[23,45,67,32,10]] #display print[array] #get the first row print[array[0]] #get the third row print[array[2]] #get the first row third element print[array[0][2]] #get the third row forth element print[array[2][3]]
Output:
[[23, 45, 43, 23, 45], [45, 67, 54, 32, 45], [89, 90, 87, 65, 44], [23, 45, 67, 32, 10]] [23, 45, 43, 23, 45] [89, 90, 87, 65, 44] 43 65
We can also access elements using for loop
Syntax:
for rows in the array:
for columns in rows:
print[columns]
where,
- rows are used to iterate the row by row
- columns is used to iterate the values present in each row.
Example:
Creare 2D array with 4 rows and 5 columns array=[[23,45,43,23,45],[45,67,54,32,45],[89,90,87,65,44],[23,45,67,32,10]] #use for loop to iterate the array for rows in array: for columns in rows: print[columns,end=" "] print[]
Output:
23 45 43 23 45 45 67 54 32 45 89 90 87 65 44 23 45 67 32 10
Inserting the values into the two-dimensional array
Here we are going to insert values into two dimensional array using insert[] function
Syntax:
array.insert[index,[values]]
where,
- the array is the input array
- the index is the row position to insert a particular row
- value are the values to be inserted into the array
Example: Insert to values in the array
#creare 2D array with 4 rows and 5 columns array=[[23,45,43,23,45],[45,67,54,32,45],[89,90,87,65,44],[23,45,67,32,10]] #insert the row at 5 th position array.insert[2, [1,2,3,4,5]] #insert the row at 6 th position array.insert[2, [1,2,3,4,5]] #insert the row at 7 th position array.insert[2, [1,2,3,4,5]] #display print[array]
Output:
[[23, 45, 43, 23, 45], [45, 67, 54, 32, 45], [1, 2, 3, 4, 5], [1, 2, 3, 4, 5], [1, 2, 3, 4, 5], [89, 90, 87, 65, 44], [23, 45, 67, 32, 10]]
Updating the values into the two-dimensional array
Here are two methods for updating values in the 2-D array[list].
You can update rows by using the following syntax
array[row_index]= [values]
You can update column values inside rows by using the following syntax
array[row_index][column_index]= [values]
Example:
#creare 2D array with 4 rows and 5 columns array=[[23,45,43,23,45],[45,67,54,32,45],[89,90,87,65,44],[23,45,67,32,10]] #update row values in the 3rd row array[2]=[0,3,5,6,7] #update row values in the 5th row array[2]=[0,3,5,6,7] #update the first row , third column array[0][2]=100 #update the second row , third column array[1][2]=400 #display print[array]
Output:
[[23, 45, 100, 23, 45], [45, 67, 400, 32, 45], [0, 3, 5, 6, 7], [23, 45, 67, 32, 10]]
Deleting the values from two-dimensional array
You can delete rows using the del function
Syntax:
del array[index]
where,
- the array is the input array
- index refers to the row index
Example:
#creare 2D array with 4 rows and 5 columns array=[[23,45,43,23,45],[45,67,54,32,45],[89,90,87,65,44],[23,45,67,32,10]] #delete row values in the 3rd row del array[2] #delete row values in the 2nd row del array[1] #display print[array]
Output:
[[23, 45, 43, 23, 45], [23, 45, 67, 32, 10]]
Get the size of two-dimensional array
You can get the size of the two-dimensional array using the line[] function. It will return the number of rows in the array
Syntax:
len[array]
Example:
Get the length of the two-dimensional array
#creare 2D array with 4 rows and 5 columns array=[[23,45,43,23,45],[45,67,54,32,45],[89,90,87,65,44],[23,45,67,32,10]] #display print[len[array]]
Output:
4
Summary:
Here are some important Array[list] Methods
| Method | Description | Syntax | Example | |
| Append[]: | This method helps us to add an element at the end to an existing array. | array.append[value] | # Adding an element using append method to the end of an array array=[1,2,3] array.append[4] print[array] Output: [1,2,3,4] | |
| Clear[]: | This method helps us to remove all the elements present in an array | array.clear[] | # Removing all the elements from an array array=[1,2,3] array.clear[] Output: [] | |
| Copy[]: | This method helps us to copy the contents of an array to a new array | array1=array.copy[] | #Copying the elements from an array to a new array array=[1,2,3] array1=[] array1=array.copy[] print[array1] Output: [1,2,3] | |
| Count[]: | This method helps us to count the no.of occurences of a an specified element in an array | array.count[element] | #Counting the no of times an element is present in an array array=[1,2,3] print[array.count[8]] Output: 0 | |
| Extend[]: | This method helps us to extend an array beyond it’s consisting elements. | array.extend[array1] | #Extending an existing array with another array array=[1,2,3] array1=[4,5,6] array.extend[array1] print[array] Output: [1,2,3,4,5,6] | |
| Index[]: | This method helps us to find the index of an element in an array | array.index[element] | #returing the index an element in an array array=[1,2,3] print[array.index[3]] Output: 2 | |
| Insert[]: | This method helps us to insert elements into an array at specified index. | array.insert[index,element] | #Inserting an element at a specified index into an array array=[1,2,3] array.insert[2,4] print[array] Output: [1,2,4,3] | |
| Pop[]: | This method helps us to remove an element at specified index | array.pop[index] | #Removing an element at specified index through pop method array=[1,2,3] array.pop[2] print[array] Output: [1,2] | |
| Remove[]: | This method helps us to remove an particular matching element in an array. | array.remove[element] | array=[1,2,3] array.remove[2] print[array] Output: [1,3] | |
| Reverse[]: | This method helps is to reverse the elements in an array. | array.reverse[] | array=[1,2,3,4] array.reverse[] print[array] Output: [4,3,2,1] |