What will be the result of the following print statements:

Code inspection

Code:

np.arange('2005-02', '2005-03', dtype='datetime64[D]')


Output:
array(['2005-02-01', '2005-02-02', '2005-02-03', '2005-02-04',
       '2005-02-05', '2005-02-06', '2005-02-07', '2005-02-08',
       '2005-02-09', '2005-02-10', '2005-02-11', '2005-02-12',
       '2005-02-13', '2005-02-14', '2005-02-15', '2005-02-16',
       '2005-02-17', '2005-02-18', '2005-02-19', '2005-02-20',
       '2005-02-21', '2005-02-22', '2005-02-23', '2005-02-24',
       '2005-02-25', '2005-02-26', '2005-02-27', '2005-02-28'],
      dtype='datetime64[D]')

Example of a datetime object in NumPy

Python's string type uses the Unicode Standard for representing characters, which lets Python programs work with all these different possible characters. Unicode (https://www.unicode.org/) is a specification that aims to list every character used by human languages and give each character its own unique code.

More on Unicode in Python

uint8 --> Unsigned integer (0 to 255)

uint16 --> Unsigned integer (0 to 65535)

uint32 --> Unsigned integer (0 to 4294967295)

uint64 --> Unsigned integer (0 to 18446744073709551615)

NumPy Unassigned Integers

Complex number, represented by two 32-bit floats (real and imaginary components)

NumPy Complex Float

NumPy allows the subtraction of two Datetime values, an operation which produces a number with a time unit. Because NumPy doesn’t have a physical quantities system in its core, the timedelta64 data type was created to complement datetime64. The arguments for timedelta64 are a number, to represent the number of units, and a date/time unit, such as (D)ay, (M)onth, (Y)ear, (h)ours, (m)inutes, or (s)econds. The timedelta64 data type also accepts the string “NAT” in place of the number for a “Not A Time” value.

NumPy Timedeltas

In python, there  is already data types that it has by default such as boolean, float, integer, etc. However, NumPy offers additional data types:

- i - integer
- b - boolean
- u - unsigned integer
- f - float
- c - complex float
- m - time delta
- M - date time
- O - object
- S - string
- U - unicode String
- V - fixed chunk of memory for other type (void)

University of Minnesota - Twin Cities

NumPy is a Python library for scientific computing that contains support for some fundamental data structures used by scikit-learn, such as multi-dimensional arrays. Example import: `import numpy as np`

NumPy

NumPy Documentation

Typically, data that's input to scikit-learn will be in the form of a NumPy array.

NumPy vs. Scikit-learn

What does the following code do?

Recall that "np.dot(a,b)" performs a matrix multiplication on a and b, whereas "a*b" performs an element-wise multiplication. Consider the two following random arrays "a" and "b": what is the shape of c?

Consider the following code: what will be c?

Consider the two following random arrays "a" and "b" below: what will be the shape of "c"?

Because the Numpy array is densely packed in memory due to its homogeneous type, Numpy gets around 30 times faster than Python.

Make big difference when handling big data.

Numpy Speed


In NumPy, there are two objects that are crucial to understanding how this library works. Those are:

1. N-dimensional array object (ndarray)

2. Universal function object (ufunc)

However, keep in mind that there are other objects that are built upon these that can be incorporated into whatever you're doing.

Fundamental Objects in NumPy

Data Types in NumPy

Within the NumPy library, there are several types of mathematical functions built-in. These functions are typically used across elements of a NumPy array.

Types of Mathematical Functions:
- Trigonometric
- Rounding
- Exponents and Logarithms
- Arithmetic
- Other Special Functions

Learn Before

Related

Learn After