[Reading notes] Python Data Analysis (12) Advanced NumPy

Da

Array: A fast and flexible homogeneous multidimensional data set container that can be used to perform some mathematical operations on the entire block of data

• Data pointers, part of system memory
• DataType Data Type/dtype
• Tuple that indicates the size of the data
• Stride:strides holds the number of bytes added to the pointer in the data store when the subscript for each axis increases by 1 o'clock
  • In [6]: Np.ones ((3,4,5), Dtype=np.float64). Strides

OUT[6]: (160, 40, 8)

Ndarray Data structure:

Reshape () function-1 parameter, the content of the dimension is automatically populated by the original content

C Vesu Fortran Order:

• : Row Order
• Fortran Order:column Order

The Ndarray of NumPy is the row order, and the reshape () and Ravel () functions accept a parameter for c/f conversion

Array refactoring

More Concise array refactoring: C_, R_c

Array Duplication/replication

Repeat: Repeats each element in an array for a specific number of times, and you can specify the number of repetitions for each element

Tile: Repeat recovery on the specified axis

Take and Put

Remove a specific element from an array

broadcasting/Broadcast

Spreads along the x-axis and spreads along the y-axis with subtle differences

Np.newaxis () Add new axis

Advanced Ufunc Usage

Ufunc is the abbreviation for universal function, which is a function that can operate on each element of an array, numpy many of the Ufunc functions are implemented at the C level, so they are computationally fast

• Np.add.reduce: Add and operate
• Np.add.accumulate: Similar to reduce, returns the same shape as the input array, saving all intermediate calculation results

• Np.multiply.outer:element-wise dot Product

user-defined functions

Frompyfunc

Structured and Record Arrays

Use Dtype to create structured tabular data, similar to the structure in C

NumPy sort

Argsort:

Lexsort: multiple sort

searchsorted

• Finds the elements in the sorted array, returns the position where the lookup value should be inserted in the array, which can make the array still orderly
• can also be used to find the position of an element within a certain interval

Speed performance:

Cpython

[Reading notes] Python Data Analysis (12) Advanced NumPy