Numpy Python Cheat Sheet



  1. Programming Cheat Sheet Pdf
  2. Numpy Python Cheat Sheet
  3. Python Numpy Array Cheat Sheet
  4. Numpy Reference Sheet

NumPy / SciPy / Pandas Cheat Sheet Select column. Select row by label. Return DataFrame index. Delete given row or column. Pass axis=1 for columns. Reindex df1 with index of df2. Reset index, putting old index in column named index. Change DataFrame index, new indecies set to NaN. Show first n rows. Show last n rows. This collection covers much more than the topics listed in the title. It also features Azure, Python, Tensorflow, data visualization, and many other cheat sheets. Python For Data Science Cheat Sheet SciPy - Linear Algebra Learn More Python for Data Science Interactively at www.datacamp.com SciPy DataCamp Learn Python for Data Science Interactively Interacting With NumPy Also see NumPy The SciPy library is one of the core packages for scientific computing that provides mathematical. NumPy is the library that gives Python its ability to work with data at speed. Originally, launched in 1995 as ‘Numeric,’ NumPy is the foundation on which many important Python data science libraries are built, including Pandas, SciPy and scikit-learn.

  • Python cheatsheet

Programming Cheat Sheet Pdf

PYTHON FOR DATA SCIENCE CHEAT SHEET Python NumPy A library consisting of multidimensional array objects and a collection of routines for processing those arrays. W h a t i s N u m P y? Import numpy as np –Import numpy I m p o r t C o n v e n t i o n FURTHERMORE: Python for Data Science Certification Training Course.

Operators¶

Command

Description

*

multiplication operation: 2*3 returns 6

**

power operation: 2**3 returns 8

@

matrix multiplication:

returns

Data Types¶

Python

Command

Description

l=[a1,a2,,an]

Constructs a list containing the objects (a1, a2,..., an). You can append to the list using l.append().The (ith) element of (l) can be accessed using l[i]

t=(a1,a2,,an)

Constructs a tuple containing the objects (a1, a2,..., an). The (ith) element of (t) can be accessed using t[i]

Built-In Functions¶

Command

Description

len(iterable)

len is a function that takes an iterable, such as a list, tuple or numpy array and returns the number of items in that object.For a numpy array, len returns the length of the outermost dimension

returns 5.

zip

Make an iterator that aggregates elements from each of the iterables.

returns [(1,4),(2,5),(3,6)]

Iterating¶

Command

Description

forainiterable:

For loop used to perform a sequence of commands (denoted using tabs) for each element in an iterable object such as a list, tuple, or numpy array.An example code is

prints [1,4,9]

Comparisons and Logical Operators¶

Command

Description

ifcondition:

Performs code if a condition is met (using tabs). For example

squares (x) if (x) is (5), otherwise cubes it.

User-Defined Functions¶

Command

Description

lambda

Used for create anonymous one line functions of the form:

The code after the lambda but before variables specifies the parameters. The code after the colon tells python what object to return.

def

The def command is used to create functions of more than one line:

The code immediately following def names the function, in this example g .The variables in the parenthesis are the parameters of the function. The remaining lines of the function are denoted by tab indents.The return statement specifies the object to be returned.

Numpy¶

Command

Description

np.array(object,dtype=None)

np.array constructs a numpy array from an object, such as a list or a list of lists.dtype allows you to specify the type of object the array is holding.You will generally note need to specify the dtype.Examples:

A[i1,i2,,in]

Access a the element in numpy array A in with index i1 in dimension 1, i2 in dimension 2, etc.Can use : to access a range of indices, where imin:imax represents all (i) such that (imin leq i < imax).Always returns an object of minimal dimension.For example,

A[:,2]

returns the 2nd column (counting from 0) of A as a 1 dimensional array and

A[0:2,:]

returns the 0th and 1st rows in a 2 dimensional array.

np.zeros(shape)

Constructs numpy array of shape shape. Here shape is an integer of sequence of integers. Such as 3, (1, 2), (2, 1), or (5, 5). Thus

np.zeros((5,5))

Constructs an (5times 5) array while

np.zeros(5,5)

will throw an error.

np.ones(shape)

Same as np.zeros but produces an array of ones

np.linspace(a,b,n)

Returns a numpy array with (n) linearly spaced points between (a) and (b). For example

np.linspace(1,2,10)

returns

np.eye(N)

Constructs the identity matrix of size (N). For example

np.eye(3)

returns the (3times 3) identity matrix:

[begin{split}left(begin{matrix}1&0&00&1&0 0&0&1end{matrix}right)end{split}]

np.diag(a)

np.diag has 2 uses. First if a is a 2 dimensional array then np.diag returns the principle diagonal of the matrix.Thus

np.diag([[1,3],[5,6]])

returns [1,6].

If (a) is a 1 dimensional array then np.diag constructs an array with $a$ as the principle diagonal. Thus,

np.diag([1,2])

returns

[begin{split}left(begin{matrix}1&00&2end{matrix}right)end{split}]

np.random.rand(d0,d1,,dn)

Constructs a numpy array of shape (d0,d1,,dn) filled with random numbers drawn from a uniform distribution between :math`(0, 1)`.For example, np.random.rand(2,3) returns

np.random.randn(d0,d1,,dn)

Same as np.random.rand(d0,d1,,dn) except that it draws from the standard normal distribution (mathcal N(0, 1))rather than the uniform distribution.

A.T

Reverses the dimensions of an array (transpose).For example,if (x = left(begin{matrix} 1& 23&4end{matrix}right)) then x.T returns (left(begin{matrix} 1& 32&4end{matrix}right))

np.hstack(tuple)

Take a sequence of arrays and stack them horizontally to make a single array. For example

returns [1,2,3,2,3,4] while

returns (left( begin{matrix} 1&22&3 3&4 end{matrix}right))

np.vstack(tuple)

Like np.hstack. Takes a sequence of arrays and stack them vertically to make a single array. For example

returns

np.amax(a,axis=None)

By default np.amax(a) finds the maximum of all elements in the array (a).Can specify maximization along a particular dimension with axis.If

a=np.array([[2,1],[3,4]])#createsa2dimarray

then

np.amax(a,axis=0)#maximizationalongrow(dim0)

returns array([3,4]) and

np.amax(a,axis=1)#maximizationalongcolumn(dim1)

returns array([2,4])

np.amin(a,axis=None)

Same as np.amax except returns minimum element.

np.argmax(a,axis=None)

Performs similar function to np.amax except returns index of maximal element.By default gives index of flattened array, otherwise can use axis to specify dimension.From the example for np.amax

returns array([1,1]) and

returns array([0,1])

np.argmin(a,axis=None)

Same as np.argmax except finds minimal index.

np.dot(a,b) or a.dot(b)

Returns an array equal to the dot product of (a) and (b).For this operation to work the innermost dimension of (a) must be equal to the outermost dimension of (b).If (a) is a ((3, 2)) array and (b) is a ((2)) array then np.dot(a,b) is valid.If (b) is a ((1, 2)) array then the operation will return an error.

numpy.linalg¶

Numpy Python Cheat Sheet

Command

Description

np.linalg.inv(A)

For a 2-dimensional array (A). np.linalg.inv returns the inverse of (A).For example, for a ((2, 2)) array (A)

returns

np.linalg.eig(A)

Returns a 1-dimensional array with all the eigenvalues of $A$ as well as a 2-dimensional array with the eigenvectors as columns.For example,

eigvals,eigvecs=np.linalg.eig(A)

returns the eigenvalues in eigvals and the eigenvectors in eigvecs.eigvecs[:,i] is the eigenvector of (A) with eigenvalue of eigval[i].

np.linalg.solve(A,b)

Constructs array (x) such that A.dot(x) is equal to (b). Theoretically should give the same answer as

but numerically more stable.

Pandas¶

Command

Description

pd.Series()

Constructs a Pandas Series Object from some specified data and/or index

pd.DataFrame()

Constructs a Pandas DataFrame object from some specified data and/or index, column names etc.

or alternatively,

Python Numpy Array Cheat Sheet

Plotting¶

Numpy Reference Sheet

Command

Description

plt.plot(x,y,s=None)

The plot command is included in matplotlib.pyplot.The plot command is used to plot (x) versus (y) where (x) and (y) are iterables of the same length.By default the plot command draws a line, using the (s) argument you can specify type of line and color.For example ‘-‘, ‘- -‘, ‘:’, ‘o’, ‘x’, and ‘-o’ reprent line, dashed line, dotted line, circles, x’s, and circle with line through it respectively.Color can be changed by appending ‘b’, ‘k’, ‘g’ or ‘r’, to get a blue, black, green or red plot respectively.For example,

plots the cosine function on the domain (0, 10) with a green line with circles at the points (x, v)