NumPy CheatSheet for Developers

Introduction-What-is-NumPy?

A library consisting of multidimensional array objects and a collection of routines for processing those arrays.

We use following shorthand in the cheat sheet:

Command	Description
`np`	import numpy library
`np.array`	The array object in NumPy
`np.array.shape`	The shape of an array is the number of elements in each dimension.
`np.array.reshape`	Reshaping means changing the shape of an array(Example 1-D to 2-D)
`np.zeros(3)`	1D array of length 3 all zeros
`np.zeros((2,3))`	2D array of all zeros
`np.zeros((3,2,4))`	3D array of all zeros
`np.full((3,4),2)`	3x4 array with all values 2
`np.random.rand(3,5)`	3x5 array of random floats between 0 and 1
`np.ones((3,4))`	3x4 array with all values 1
`np.eye(4)`	4x4 array of 0 with 1 on diagonal

NumPy has some extra data types, and refer to data types with one character, like i for integers, u for unsigned integers etc.

Below is a list of all data types in NumPy and the characters used to represent them.

Command	Description
`i`	integer
`b`	boolean
`u`	unsigned integer
`f`	float
`c`	complex float
`m`	timedelta
`M`	datetime
`O`	object
`S`	string
`U`	unicode string
`V`	fixed chunk of memory for other type ( void )

Command	Description
`np.loadtxt('New_file.txt')`	From a text file
`np.genfromtxt('New_file.csv',delimiter=',')`	From a CSV file
`np.savetxt('New_file.txt',arr,delimiter=' ')`	Writes to a text file
`np.savetxt('New_file.csv',arr,delimiter=',')`	Writes to a CSV file

Command	Description
`array.size`	Returns number of elements in array
`array.shape`	Returns dimensions of array(rows,columns)
`array.dtype`	Returns type of elements in array

Keywords	Description	Action
`np.copy(array)`	Copies array to new memory array.	Copying
`view(dtype)`	Creates view of array elements with type dtype	Copying
`array.sort()`	Sorts array	Sorting
`array.sort(axis=0)`	Sorts specific axis of array	Sorting
`array.reshape(2,3)`	Reshapes array to 2 rows, 3 columns without changing data.	Sorting
`np.append(array,values)`	Appends values to end of array	Adding
`np.insert(array,4,values)`	Inserts values into array before index 4	Adding
`np.delete(array,2,axis=0)`	Deletes row on index 2 of array	Removing
`np.delete(array,3,axis=1)`	Deletes column on index 3 of array	Removing
`np.concatenate((array1,array2),axis=0)`	Adds array2 as rows to the end of array1	Combining
`np.concatenate((array1,array2),axis=1)`	Adds array2 as columns to end of array1	Combining
`np.split(array,3)`	Splits array into 3 sub	arrays
`a[0]=5`	Assigns array element on index 0 the value 5	Indexing
`a[2,3]=1`	Assigns array element on index [2][3] the value 1	Indexing
`a[2]`	Returns the element of index 2 in array a.	Subseting
`a[3,5]`	Returns the 2D array element on index [3][5]	Subseting
`a[0:4]`	Returns the elements at indices 0,1,2,3	Slicing
`a[0:4,3]`	Returns the elements on rows 0,1,2,3 at column 3	Slicing
`a[:2]`	Returns the elements at indices 0,1	Slicing
`a[:,1]`	Returns the elements at index 1 on all rows	Slicing