Install
After downloaded the Numpy into C:\Python27\Scripts.
pip2.7 install [path_of_numpy_whl]
Basic Knowledges
- Import all modules within Numpy into the current namespace.
from numpy import *
- Change the current directory within IDLE development environment.
import os
os.getcwd() # obtain the current directory
os.chdir("D:\\test") # change directory
os.chdir('D:\\test') # no difference between ' and ''
axis
For 2-D array,axis=0means processing according to the vertical axis, whileaxis=1means the horizontal axis.
For N-D array, 'axis=i' means Numpy will process the array according to the i-th subscript.sort, sorted & argsort
sort
After sorting process, the original array will be sorted.
>>> a = [1,2,1,4,3,5] >>> a.sort() >>> a [1, 1, 2, 3, 4, 5]sorted(iterable, cmp, key, reverse)
After sorting process, the original array will not be influenced.
>>> a = [1,2,1,4,3,5] >>> sorted(a) [1, 1, 2, 3, 4, 5] >>> a [1, 2, 1, 4, 3, 5]argsort
Return index of array according to ascending values.
Advanced Knowledges
- Save a numpy matrix into a txt file.
# np.savetxt(FileName, saveMatdData, format, delimiter, newline)
np.savetxt('s12.txt', data, fmt='%f', delimiter=' ', newline='\n')
- Save a numpy matrix into a csv file.
# np.savetxt(FileName, saveMatdData, delimiter)
np.savetxt('s13.csv', data, delimiter=',')
- Load a csv file into a
ndarray.
# np.loadtxt(open(csvFileName,'rb'), delimiter, skiprows)
np.loadtxt(open('s13.csv','rb'), delimiter=',', skiprows=0)
- Load a csv file into a numpy matrix.
np.mat(np.loadtxt(open('s13.csv','rb'), delimiter=',', skiprows=0))
Reference
Python IDLE或shell中切换路径
numpy模块之axis
Python中排序常用到的sort 、sorted和argsort函数
