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What is argmin in NumPy?

The numpy. argmin() method returns indices of the min element of the array in a particular axis. Syntax : numpy.argmin(array, axis = None, out = None)

How does argmin work in Python?

Numpy argmin is a function in python which returns the index of the minimum element from a given array along the given axis. The function takes an array as the input and outputs the index of the minimum element. What is this? The input array can be a single-dimensional array as well as a multi-dimensional array.

How do you find the index of min value in NumPy?

numpy. amin() | Find minimum value in Numpy Array and it’s index
  1. If it’s provided then it will return for array of min values along the axis i.e.
  2. If axis=0 then it returns an array containing min value for each columns.
  3. If axis=1 then it returns an array containing min value for each row.

How do I remove an element from a NumPy array?

To remove an element from a NumPy array:
  1. Specify the index of the element to remove.
  2. Call the numpy. delete() function on the array for the given index.

How do you reshape an array in Numpy?

In order to reshape a numpy array we use reshape method with the given array.
  1. Syntax : array.reshape(shape)
  2. Argument : It take tuple as argument, tuple is the new shape to be formed.
  3. Return : It returns numpy.ndarray.

What is Argmax in probability?

Argmax is an operation that finds the argument that gives the maximum value from a target function. Argmax is most commonly used in machine learning for finding the class with the largest predicted probability.

What are axis in Numpy?

Axes are defined for arrays with more than one dimension. A 2-dimensional array has two corresponding axes: the first running vertically downwards across rows (axis 0), and the second running horizontally across columns (axis 1). Many operation can take place along one of these axes.

What is the syntax for Range function?

Python range() Function

The range() function returns a sequence of numbers, starting from 0 by default, and increments by 1 (by default), and stops before a specified number.

How do you find min and max in numpy?

max(“array name”) function. For finding the minimum element use numpy. min(“array name”) function.

How do you find the minimum and maximum value in python?

Use Python’s min() and max() to find smallest and largest values in your data. Call min() and max() with a single iterable or with any number of regular arguments. Use min() and max() with strings and dictionaries.

How do you check the index of an item in a list python?

To find the index of an element in a list, you use the index() function. It returns 3 as expected.

How do you remove specific elements from an array in Python?

For removing an element from an array, developers can also use the pop() method of the array. If we simply use pop() without passing any parameter, then it will remove the element from the last (n th) index. But if we specify the index value of the array, it will remove that particular element from the array.

How do you remove certain values from an array in Python?

Removing Python Array Elements

We can delete one or more items from an array using Python’s del statement. We can use the remove() method to remove the given item, and pop() method to remove an item at the given index.

How do I remove items from my list?

The del operator removes the item or an element at the specified index location from the list, but the removed item is not returned, as it is with the pop() method.

There are three ways in which you can Remove elements from List:
  1. Using the remove() method.
  2. Using the list object’s pop() method.
  3. Using the del operator.

What is the meaning of ArgMin?

ArgMin is typically used to find the smallest possible values given constraints. In different areas, this may be called the best strategy, best fit, best configuration and so on. If f and cons are linear or polynomial, ArgMin will always find a global minimum.

What are axis in NumPy?

Axes are defined for arrays with more than one dimension. A 2-dimensional array has two corresponding axes: the first running vertically downwards across rows (axis 0), and the second running horizontally across columns (axis 1). Many operation can take place along one of these axes.

How do you stack arrays in NumPy?

  1. numpy. stack() function is used to join a sequence of same dimension arrays along a new axis. The axis parameter specifies the index of the new axis in the dimensions of the result. For example, if axis=0 it will be the first dimension and if axis=-1 it will be the last dimension.
  2. Code #1 :
  3. Code #2 :

How do you find the index of the smallest number in an array?

To get the index of the min value in an array:
  1. Get the min value in the array, using the Math. min() method.
  2. Call the indexOf() method on the array, passing it the min value.
  3. The indexOf method returns the index of the first occurrence of the value in the array or -1 if the value is not found.

38. argmax and argmin in Numpy
38. argmax and argmin in Numpy


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What is numpy argmin

Syntax of Numpy argmin

Parameters of Numpy argmin

Return Value of Numpy argmin

Numpy argmin() for 1D array

Argmin() for multi dimensional array

Numpy Argmin with different axis values

Numpy argmin with Condition

Numpy Argmin with Matrix

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Syntax of Numpy argmin

Parameters of Numpy argmin

Return Value of Numpy argmin

Numpy argmin() for 1D array

Argmin() for multi dimensional array

Numpy Argmin with different axis values

Numpy argmin with Condition

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np.argmin: How to Find Index of Minimum Element in Array

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NumPy np.argmin()

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numpy.argmin() in Python

The numpy.argmin() method returns indices of the min element of the array in a particular axis.

Syntax :

numpy.argmin(array, axis = None, out = None)

Parameters :

array : Input array to work on axis : [int, optional]Along a specified axis like 0 or 1 out : [array optional]Provides a feature to insert output to the out array and it should be of appropriate shape and dtype

Return :

Array of indices into the array with same shape as array.shape with the dimension along axis removed.

Code 1 :

Python

import numpy as geek array = geek.arange( 8 ) print ( “INPUT ARRAY :

” , array) print ( ”

Indices of min element : ” , geek.argmin(array, axis = 0 ))

Output :

INPUT ARRAY : [0 1 2 3 4 5 6 7] Indices of min element : 0

Code 2 :

Python

import numpy as geek array = geek.random.randint( 16 , size = ( 4 , 4 )) print ( “INPUT ARRAY :

” , array) print ( ”

Indices of min element : ” , geek.argmin(array, axis = 0 ))

Output :

INPUT ARRAY : [[ 8 13 5 0] [ 0 2 5 3] [10 7 15 15] [ 3 11 4 12]] Indices of min element : [1 1 3 0]

Code 3 :

Python

import numpy as geek array = geek.arange( 10 ).reshape( 2 , 5 ) print ( “array :

” , array) array[ 0 ][ 0 ] = 10 array[ 1 ][ 1 ] = 1 array[ 0 ][ 1 ] = 1 print ( ”

array :

” , array) print ( ”

array : ” , geek.argmin(array)) print ( ”

min ELEMENT INDICES : ” , geek.argmin(array, axis = 0 ))

Output :

array : [[0 1 2 3 4] [5 6 7 8 9]] array : [[10 1 2 3 4] [ 5 1 7 8 9]] array : 1 min ELEMENT INDICES : [1 0 0 0 0]

References :

https://docs.scipy.org/doc/numpy-dev/reference/generated/numpy.argmin.html#numpy.argmin

Note :

These codes won’t run on online IDE’s. Please run them on your systems to explore the working

.

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Know About Numpy argmin Function in Python

Numpy stands for Numerical Python. With numpy, we can perform mathematical computations at high speed in python. The Numpy library in python consists of a large collection of high-level mathematical functions. These functions are used for handling large, multi-dimensional arrays and matrices in python and for performing various logical and statistical operations on them. Out of the many available functions in numpy, we shall be looking into one such function – Numpy Argmin.

What is numpy argmin?

Numpy argmin is a function in python which returns the index of the minimum element from a given array along the given axis. The function takes an array as the input and outputs the index of the minimum element.

The input array can be a single-dimensional array as well as a multi-dimensional array. We can also perform sorting on the array using this argmin function.

Syntax of Numpy argmin

The syntax of the numpy argmin function is:

numpy.argmin(a, axis=None, out=None)

The function accepts three parameters – a, axis and out.

Parameters of Numpy argmin:

a: It is the array like input given to the function. It is the array for which the index of the minimum element has to be found.

axis: It is an optional parameter which takes an integer value. If not specified, then it is None by default. If specified, then the minimum value’s index is returned along that axis.

out: This is also an optional parameter. If it is provided, then the result of the argmin function will be stored into this array. But, the given array’s size should be compatible with the return array’s shape.

Return Value of Numpy argmin:

index_array: It is an array containing integer values. These integer values contain the index(s) of the minimum value along the given axis.

Numpy argmin() for 1D array

Let us understand with some python code how to use the argmin() function. First, we shall import the numpy library.

import numpy as np

Now, we shall take a numpy array and store it into a variable named ‘array’.

array = np.array([10,7,2,1,5,8,11,9])

After creating the array, we shall pass the ‘array’ as an argument to the argmin() function. Then, we shall print the return value of that function.

print(np.argmin(array))

The output is:

3

The minimum value in the array is 1. Since the indexing starts from 0, the index of 1 – which is 3 – shall be returned by the function.

The Entire Code is:

import numpy as np array = np.array([10,7,2,1,5,8,11,9]) print(np.argmin(array))

Argmin() for multi dimensional array

We can also use the argmin function to calculate the minimum value for a multi dimensional array. The output will be calculate along the axis of the multi dimensional array.

Let us take a two dimensional array first.

import numpy as np array = np.array([[10,7,2,1],[5,8,11,9]])

Now, we shall pass the array to the argmin function. We will not be mentioning the ‘axis’ parameter explicitly.

So, axis will have its default value – ‘None’.

print(np.argmin(array))

Since the ‘axis’ is ‘None’, the output will be the index of the element in the form of a flattened array.

Output:

3

The answer is similar to that obtained in case of the one dimensional array.

The Entire Code is:

import numpy as np array = np.array([[10,7,2,1],[5,8,11,9]]) print(np.argmin(array))

Numpy Argmin with different axis values

Now, we shall try to change the axis values of the argmin function and see how it changes the output.

Earlier, we were using axis = None. Now we shall first try for axis = 0. We shall take the same two dimensional array as before.

Axis = 0:

import numpy as np array = np.array([[10,7,2,1],[5,8,11,9]])

Now, in the argmin function, we shall pass ‘axis = 0’ as the second argument.

print(np.argmin(array, axis = 0))

The output will contain an array with the index value of the minimum element for each column of the 2D array.

[1 0 0 0]

In the first column, between 10 and 5, 5 is minimum. So, the index value of 5,which is 1, shall be passed. Similarly the index value for the other elements shall be passed too.

The Entire Code is:

import numpy as np array = np.array([[10,7,2,1],[5,8,11,9]]) print(np.argmin(array, axis = 0))

Axis = 1:

Now, we shall pass axis = 1 instead of axis = 0.

import numpy as np array = np.array([[10,7,2,1],[5,8,11,9]]) print(np.argmin(array, axis = 1))

The output will be an array containing indexes of minimum elements along the row of the two dimensional array.

[3 0]

So, in the first row, the minimum element is at position 3 and in the second row, minimum element is at position 0.

Numpy argmin with Condition

We can also apply argmin() function for a given array where the elements fulfill a certain condition. For this, we shall be making use of Masked Arrays in numpy. Masked Arrays are those arrays where the array elements may be invalid entries.

For all the elements which do not fulfill the given condition, we shall mask them and not consider them. Then for the rest of the elements, the index of the minimum value shall be returned.

Here, we shall only include those elements whose value is greater than or equal to 6. So in the MaskedArray, we shall pass the opposite condition, i.e., the elements whose value is less than 6 in order to mask those elements.

import numpy as np array = np.array([10,7,2,1,5,8,11,9]) array = np.ma.MaskedArray(array, array<6) print(array) The printed elements would look something like this: [10 7 -- -- -- 8 11 9] Now, we shall print the np.argmin() function’s return value. print(np.argmin(array)) Since out of the unmasked elements 7 has the minimum value, its index 1 would be printed. 1 The Entire Code is: import numpy as np array = np.array([10,7,2,1,5,8,11,9]) array = np.ma.MaskedArray(array, array<6) print(array) print(np.argmin(array)) Numpy Argmin with Matrix We can also use the argmin function to find an index of minimum elements from a matrix. For that, we will access it using the Syntax: numpy.matrix.argmin We shall create a matrix using numpy’s matrix function. import numpy as np matrix = np.matrix(np.arange(16).reshape((4,4))) print(matrix) print(matrix.argmin()) The output is: [[ 0 1 2 3] [ 4 5 6 7] [ 8 9 10 11] [12 13 14 15]] 0 Here, 0 is printed as the index of the minimum value 0. Also, Read Numpy argmin FAQ Here are a few questions we hear often when talking about Numpy argmin. How to handle nan values while using numpy array? We can mask the nan values present in a given array using the MaskedArray. All the nan values will be masked and not considered for the argmin function. The code is : import numpy as np array = np.array([10, np.nan,2, np.nan,5,8, np.nan,9]) array = np.ma.MaskedArray(array, np.isnan(array)) print(array) print(np.argmin(array)) The output is: [10.0 — 2.0 — 5.0 8.0 — 9.0] 2 This sums up everything about Numpy Argmin. If you have any questions, let us know in the comments below. Until next time, Keep Learning!

numpy.delete: How to Remove Elements from a NumPy Array

To remove an element from a NumPy array:

Specify the index of the element to remove. Call the numpy.delete() function on the array for the given index.

For example:

import numpy as np arr = np.array([1, 2, 3, 4, 5]) index = 0 arr = np.delete(arr, index) print(arr)

Output:

[2 3 4 5]

This is the quick answer.

However, there is a lot more when it comes to removing elements from a NumPy array.

In this guide, you are going to learn how to:

Remove elements from 1D arrays.

Remove elements from 2D arrays.

Use the axis to remove entire rows/columns.

Remove a specific element by a value.

How Does numpy.delete() Work

In NumPy, there is a built-in function numpy.delete() you can use to remove elements from an array.

The syntax of numpy.delete() is:

numpy.delete(arr, obj, axis=None)

Where:

arr is the input array from which you want to remove elements.

is the input array from which you want to remove elements. obj specifies the index or indices at which you want to remove elements.

specifies the index or indices at which you want to remove elements. axis is an optional parameter that specifies the axis along which to remove the elements. By default it is None. In this case, the obj is applied to a flattened version of the arr.

The numpy.delete() function returns a copy of the original array arr.

Now that you understand how the numpy.delete() function works, let’s see common use cases for it.

1D NumPy Arrays

When it comes to removing elements, dealing with 1D arrays is easy. You do not need to worry about the axis parameter. All you need to do is to specify the index or indices at which you want to remove an element or multiple elements.

Let’s see some useful examples.

How to Remove a Single Element

To delete a single element from a 1D NumPy array:

Specify the index at which you want to remove the element. Call the numpy.delete() function on the array with the specified index.

For example, let’s remove the 3rd element from an array of numbers:

import numpy as np arr = np.array([1, 2, 3, 4, 5]) arr = np.delete(arr, 2) print(arr)

Output:

[1 2 4 5]

Now that you handle removing single elements, let’s take a look at how you can remove multiple elements in one go.

How to Remove Multiple Elements

One way to remove multiple elements from a NumPy array is by calling the numpy.delete() function repeatedly for a bunch of indices.

However, this introduces unnecessary repetition.

The correct way to remove multiple elements is to:

Add the indices to a sequence, such as a list. Call the numpy.delete() function on the array with the given index sequence.

For example, let’s remove the first, second, and third elements from an array of strings:

import numpy as np arr = np.array([“Alice”, “Bob”, “Charlie”, “David”, “Eric”]) arr = np.delete(arr, [0, 1, 2]) print(arr)

Output:

[‘David’ ‘Eric’]

At this point, you understand how to remove elements from a 1D array.

Next, let’s move up to the 2nd dimension.

2D NumPy Arrays

Removing elements from a 2D NumPy array is almost as easy as removing elements from a 1D one.

However, when it comes to 2D arrays, you may want to remove:

A single element

Multiple elements

A single row

Multiple rows

A single column

Multiple columns

Removing columns and rows means you have to specify the optional axis parameter.

Let’s see some useful examples to support understanding.

How to Remove a Column

To delete a column from a 2D NumPy array:

Specify the index of the column you want to remove. Set the axis parameter to 1. Call the numpy.delete() function with the desired column index and axis.

For example, let’s remove the 2nd column from a 2D array:

import numpy as np arr = np.array([[1 ,2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]) arr = np.delete(arr, 1, axis=1) print(arr)

Output:

[[ 1 3 4] [ 5 7 8] [ 9 11 12]]

Now that you understand how to remove a single column, let’s take a look at how to remove multiple columns.

How to Remove Multiple Columns

One way to remove multiple columns is to repeat the process of removing one column for each column.

However, this is not the optimal way to do things.

To remove multiple columns from a 2D NumPy array:

Specify all the columns you want to remove as a sequence, such as a list. Set the axis 1. Call the numpy.delete() function for the given column indexes and axis.

For example, let’s remove the first and the last column of the array of numbers:

import numpy as np arr = np.array([[1 ,2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]) arr = np.delete(arr, [0,3], axis=1) print(arr)

Output:

[[ 2 3] [ 6 7] [10 11]]

Now you understand how to remove columns from a NumPy array. The logical next step is to learn how to remove rows.

How to Remove a Row

To delete a row from a 2D NumPy array:

Specify the index of the row you want to delete. Set the axis at 0 to touch the rows. Call the numpy.delete() function on the given row index for the 0 axis.

For example, let’s remove the first row in an array of numbers:

import numpy as np arr = np.array([[1 ,2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]) arr = np.delete(arr, 0, axis=0) print(arr)

Output:

[[ 5 6 7 8] [ 9 10 11 12]]

Now that you understand how to remove a row from a NumPy array, let’s take a look at how to remove multiple rows at the same go.

How to Remove Multiple Rows

To delete multiple rows from a NumPy array, you could repeat the above process of removing a single row for each row you want to remove.

However, this is not the best way to do it.

To remove multiple rows from a 2D NumPy array:

Specify the indices of the rows to be deleted as a sequence, such as a list. Set the axis at 0 to affect rows. Call the numpy.delete() function for the set of indices and the axis.

For example, let’s remove the first and the last row from an array of numbers.

import numpy as np arr = np.array([[1 ,2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]) arr = np.delete(arr, [0, 2], axis=0) print(arr)

Output:

[[5 6 7 8]]

Now you understand how to remove rows and columns.

Last but not least, let’s take a look at how to remove a specific element from a NumPy array by value.

How to Remove a Specific NumPy Array Element by Value

Sometimes you might want to remove specific elements or elements from a NumPy array.

To remove a specific element from a NumPy array by value:

Call the numpy.delete() function. Use numpy.where() function as the second argument to specify the removing criterion.

For example, let’s remove all 1s from an array of numbers:

import numpy as np arr = np.array([1, 1, 1, 1, 2, 3, 4]) arr = np.delete(arr, np.where(arr == 1)) print(arr)

Output:

[2 3 4]

Conclusion

Today you learned how to remove elements from NumPy arrays.

To recap, whenever you want to remove an element, call the numpy.delete() function for a given index.

If you are working with multidimensional arrays and want to delete entire columns/rows, specify the optional axis parameter.

For example, with 2D arrays, axis=1 affects columns, and axis=0 touches the rows.

Thanks for reading.

Happy coding!

Further Reading

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