Beginner NumPy (iii)

Boolean index

1 #!/usr/bin/env python2 #-*-coding:utf-8-*-3 " "4 Description: Beginner NumPy (iii)--Boolean index5 Created on October 8, 20156 @author: Zenwan7 @version:8 " "9 ImportNumPy as NPTen  fromPprintImportPprint One  Anames = Np.array (['Beijing','Anhui','Shanghai','Jiangsu','Zhejiang','Shanghai','Anhui'])#There are duplicates -data = Np.random.randn (7,4)#generate random numbers for normal distributions - pprint (names) the pprint (data) -  - " " - suppose each name in the names corresponds to a row in the data array, and we want to select all the rows that correspond to the name ' Shanghai '.  + we want to select all the data rows that correspond to ' Shanghai '. - As with arithmetic operations, the array's comparison operations (such as = =) are also vectorized, so the array names and the string ' Shanghai ' comparison operations produce a Boolean array arr_bool, + This type of Boolean array can be used for the group index A " " atArr0_bool = (Names = ='Shanghai')#array-to-string comparison operations produce a Boolean array -Pprint (Arr0_bool)#array ([False, False, True, False, False, True, false], Dtype=bool) - Pprint (Data[arr0_bool]) -  - #Mix Boolean arrays with slices, integers, integer sequences, and more -Pprint (Data[names = ='Shanghai', 2:]) inPprint (Data[names = ='Shanghai', 3]) -  to #Select other combinations of values other than ' Shanghai ' +Arr1_bool = (Names! ='Shanghai') -Arr2_bool = ((Names! ='Shanghai')| (names=='Jiangsu')) theArr2_bool = ((Names! ='Shanghai') & (names=='Jiangsu')) *  $ #set all positive numbers in data to-1Panax NotoginsengData[data > 0] = 1#The comparison operation of the array is vectorized - pprint (data) the  + #set a certificate row or column through a one-dimensional Boolean array, such as setting the entire row of data for ' Shanghai ' to 0 Adata [names = ='Shanghai'] =0 thePprint (data)

Operation Result:

1Array (['Beijing','Anhui','Shanghai','Jiangsu','Zhejiang','Shanghai',2        'Anhui'], 3Dtype='| S8')4Array ([[[0.84608482, 0.51050985,-0.43504218,-1.08530829],5[0.51865817,-1.0914367,-0.6953841,-1.59947846],6[-0.9308739,-0.2748063,-0.410821,-1.66078485],7[0.2290689,-0.85357479,-0.42896687, 0.97397006],8[-0.60247776,-0.24399895,-1.03297297,-0.76709796],9[-0.31226921,-0.42020231, 1.12008391, 0.54366616],Ten[0.53271514, 0.50497622, 1.02203728,-0.12969158]]) OneArray ([False, False, True, False, False, True, false], dtype=bool) AArray ([[-0.9308739,-0.2748063,-0.410821,-1.66078485], -[-0.31226921,-0.42020231, 1.12008391, 0.54366616]]) -Array ([[-0.410821,-1.66078485], the[1.12008391, 0.54366616]]) -Array ([-1.66078485, 0.54366616]) -Array ([[-1].        ,-1. ,-0.43504218,-1.08530829], -[-1. ,-1.0914367,-0.6953841,-1.59947846], +[-0.9308739,-0.2748063,-0.410821,-1.66078485], -[-1. ,-0.85357479,-0.42896687,-1. ], +[-0.60247776,-0.24399895,-1.03297297,-0.76709796], A[-0.31226921,-0.42020231,-1. ,-1. ], at[-1.        ,-1.        ,-1. ,-0.12969158]]) -Array ([[-1].        ,-1. ,-0.43504218,-1.08530829], -[-1. ,-1.0914367,-0.6953841,-1.59947846], - [0., 0.        , 0.        , 0. ], -[-1. ,-0.85357479,-0.42896687,-1. ], -[-0.60247776,-0.24399895,-1.03297297,-0.76709796], in [0., 0.        , 0.        , 0. ], -[-1.        ,-1.        ,-1. ,-0.12969158]])

Beginner NumPy (iii)