@@ -503,74 +503,74 @@ <h3>1. np数组的构造<a class="headerlink" href="#np" title="Permalink to thi
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< p > 【c】随机矩阵: < code class ="docutils literal notranslate "> < span class ="pre "> np.random</ span > </ code > </ p >
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< p > 最常用的随机生成函数为 < code class ="docutils literal notranslate "> < span class ="pre "> rand,</ span > < span class ="pre "> randn,</ span > < span class ="pre "> randint,</ span > < span class ="pre "> choice</ span > </ code > ,它们分别表示0-1均匀分布的随机数组、标准正态的随机数组、随机整数组和随机列表抽样:</ p >
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< div class ="highlight-ipython notranslate "> < div class ="highlight "> < pre > < span > </ span > < span class ="gp "> In [38]: </ span > < span class ="n "> np</ span > < span class ="o "> .</ span > < span class ="n "> random</ span > < span class ="o "> .</ span > < span class ="n "> rand</ span > < span class ="p "> (</ span > < span class ="mi "> 3</ span > < span class ="p "> )</ span > < span class ="c1 "> # 生成服从0-1均匀分布的三个随机数</ span >
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- < span class ="gh "> Out[38]: </ span > < span class ="go "> array([0.71621444 , 0.26429503 , 0.5954694 ])</ span >
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+ < span class ="gh "> Out[38]: </ span > < span class ="go "> array([0.99390903 , 0.25854328 , 0.13560598 ])</ span >
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< span class ="gp "> In [39]: </ span > < span class ="n "> np</ span > < span class ="o "> .</ span > < span class ="n "> random</ span > < span class ="o "> .</ span > < span class ="n "> rand</ span > < span class ="p "> (</ span > < span class ="mi "> 3</ span > < span class ="p "> ,</ span > < span class ="mi "> 3</ span > < span class ="p "> )</ span > < span class ="c1 "> # 注意这里传入的不是元组,每个维度大小分开输入</ span >
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< span class ="gh "> Out[39]: </ span > < span class ="go "> </ span >
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- < span class ="go "> array([[0.04536995 , 0.64963898 , 0.79417025 ],</ span >
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- < span class ="go "> [0.1394991 , 0.54557398 , 0.35203454 ],</ span >
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- < span class ="go "> [0.37110594 , 0.20289376 , 0.27176637 ]])</ span >
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+ < span class ="go "> array([[0.62634822 , 0.06747959 , 0.76049576 ],</ span >
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+ < span class ="go "> [0.21826591 , 0.71708638 , 0.98481069 ],</ span >
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+ < span class ="go "> [0.38071365 , 0.82645691 , 0.25598288 ]])</ span >
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</ pre > </ div >
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</ div >
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< p > 对于服从区间 < span class ="math notranslate nohighlight "> \(a\)</ span > 到 < span class ="math notranslate nohighlight "> \(b\)</ span > 上的均匀分布可以如下生成:</ p >
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< div class ="highlight-ipython notranslate "> < div class ="highlight "> < pre > < span > </ span > < span class ="gp "> In [40]: </ span > < span class ="n "> a</ span > < span class ="p "> ,</ span > < span class ="n "> b</ span > < span class ="o "> =</ span > < span class ="mi "> 5</ span > < span class ="p "> ,</ span > < span class ="mi "> 15</ span >
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< span class ="gp "> In [41]: </ span > < span class ="p "> (</ span > < span class ="n "> b</ span > < span class ="o "> -</ span > < span class ="n "> a</ span > < span class ="p "> )</ span > < span class ="o "> *</ span > < span class ="n "> np</ span > < span class ="o "> .</ span > < span class ="n "> random</ span > < span class ="o "> .</ span > < span class ="n "> rand</ span > < span class ="p "> (</ span > < span class ="mi "> 3</ span > < span class ="p "> )</ span > < span class ="o "> +</ span > < span class ="n "> a</ span >
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- < span class ="gh "> Out[41]: </ span > < span class ="go "> array([ 6.5379111 , 11.12207163, 13.63008547 ])</ span >
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+ < span class ="gh "> Out[41]: </ span > < span class ="go "> array([ 6.40061821, 6.72343487, 10.49412407 ])</ span >
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</ pre > </ div >
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</ div >
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< p > 一般的,可以选择已有的库函数:</ p >
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< div class ="highlight-ipython notranslate "> < div class ="highlight "> < pre > < span > </ span > < span class ="gp "> In [42]: </ span > < span class ="n "> np</ span > < span class ="o "> .</ span > < span class ="n "> random</ span > < span class ="o "> .</ span > < span class ="n "> uniform</ span > < span class ="p "> (</ span > < span class ="mi "> 5</ span > < span class ="p "> ,</ span > < span class ="mi "> 15</ span > < span class ="p "> ,</ span > < span class ="mi "> 3</ span > < span class ="p "> )</ span >
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- < span class ="gh "> Out[42]: </ span > < span class ="go "> array([10.79115056, 13.92675102, 13.29722678 ])</ span >
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+ < span class ="gh "> Out[42]: </ span > < span class ="go "> array([11.10830186, 7.35193797, 8.46971257 ])</ span >
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</ pre > </ div >
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</ div >
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< p > < code class ="docutils literal notranslate "> < span class ="pre "> randn</ span > </ code > 生成了 < span class ="math notranslate nohighlight "> \(N\rm{(\mathbf{0}, \mathbf{I})}\)</ span > 的标准正态分布:</ p >
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< div class ="highlight-ipython notranslate "> < div class ="highlight "> < pre > < span > </ span > < span class ="gp "> In [43]: </ span > < span class ="n "> np</ span > < span class ="o "> .</ span > < span class ="n "> random</ span > < span class ="o "> .</ span > < span class ="n "> randn</ span > < span class ="p "> (</ span > < span class ="mi "> 3</ span > < span class ="p "> )</ span >
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- < span class ="gh "> Out[43]: </ span > < span class ="go "> array([-0.83503946, 0.16748577 , 0.37559476 ])</ span >
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+ < span class ="gh "> Out[43]: </ span > < span class ="go "> array([ 1.2642241 , -1.04640246 , 0.05297258 ])</ span >
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< span class ="gp "> In [44]: </ span > < span class ="n "> np</ span > < span class ="o "> .</ span > < span class ="n "> random</ span > < span class ="o "> .</ span > < span class ="n "> randn</ span > < span class ="p "> (</ span > < span class ="mi "> 2</ span > < span class ="p "> ,</ span > < span class ="mi "> 2</ span > < span class ="p "> )</ span >
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< span class ="gh "> Out[44]: </ span > < span class ="go "> </ span >
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- < span class ="go "> array([[ 0.54820762, -0.62745115 ],</ span >
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- < span class ="go "> [-0.98555211, -0.76136085 ]])</ span >
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+ < span class ="go "> array([[2.65755302, 0.12266858 ],</ span >
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+ < span class ="go "> [0.29899713, 0.40504878 ]])</ span >
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</ pre > </ div >
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</ div >
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< p > 对于服从方差为 < span class ="math notranslate nohighlight "> \(\sigma^2\)</ span > 均值为 < span class ="math notranslate nohighlight "> \(\mu\)</ span > 的一元正态分布可以如下生成:</ p >
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< div class ="highlight-ipython notranslate "> < div class ="highlight "> < pre > < span > </ span > < span class ="gp "> In [45]: </ span > < span class ="n "> sigma</ span > < span class ="p "> ,</ span > < span class ="n "> mu</ span > < span class ="o "> =</ span > < span class ="mf "> 2.5</ span > < span class ="p "> ,</ span > < span class ="mi "> 3</ span >
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< span class ="gp "> In [46]: </ span > < span class ="n "> mu</ span > < span class ="o "> +</ span > < span class ="n "> np</ span > < span class ="o "> .</ span > < span class ="n "> random</ span > < span class ="o "> .</ span > < span class ="n "> randn</ span > < span class ="p "> (</ span > < span class ="mi "> 3</ span > < span class ="p "> )</ span > < span class ="o "> *</ span > < span class ="n "> sigma</ span >
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- < span class ="gh "> Out[46]: </ span > < span class ="go "> array([-0.44611022, 5.298121 , 6.83720049 ])</ span >
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+ < span class ="gh "> Out[46]: </ span > < span class ="go "> array([6.46031228, 0.57297935, 5.2692226 ])</ span >
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</ pre > </ div >
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</ div >
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< p > 同样的,也可选择从已有函数生成:</ p >
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< div class ="highlight-ipython notranslate "> < div class ="highlight "> < pre > < span > </ span > < span class ="gp "> In [47]: </ span > < span class ="n "> np</ span > < span class ="o "> .</ span > < span class ="n "> random</ span > < span class ="o "> .</ span > < span class ="n "> normal</ span > < span class ="p "> (</ span > < span class ="mi "> 3</ span > < span class ="p "> ,</ span > < span class ="mf "> 2.5</ span > < span class ="p "> ,</ span > < span class ="mi "> 3</ span > < span class ="p "> )</ span >
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- < span class ="gh "> Out[47]: </ span > < span class ="go "> array([ 7.1350261 , -0.27804915, 2.36612487 ])</ span >
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+ < span class ="gh "> Out[47]: </ span > < span class ="go "> array([2.72546019, 7.42390272, 3.71079215 ])</ span >
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</ pre > </ div >
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</ div >
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< p > < code class ="docutils literal notranslate "> < span class ="pre "> randint</ span > </ code > 可以指定生成随机整数的最小值最大值(不包含)和维度大小:</ p >
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< div class ="highlight-ipython notranslate "> < div class ="highlight "> < pre > < span > </ span > < span class ="gp "> In [48]: </ span > < span class ="n "> low</ span > < span class ="p "> ,</ span > < span class ="n "> high</ span > < span class ="p "> ,</ span > < span class ="n "> size</ span > < span class ="o "> =</ span > < span class ="mi "> 5</ span > < span class ="p "> ,</ span > < span class ="mi "> 15</ span > < span class ="p "> ,</ span > < span class ="p "> (</ span > < span class ="mi "> 2</ span > < span class ="p "> ,</ span > < span class ="mi "> 2</ span > < span class ="p "> )</ span > < span class ="c1 "> # 生成5到14的随机整数</ span >
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< span class ="gp "> In [49]: </ span > < span class ="n "> np</ span > < span class ="o "> .</ span > < span class ="n "> random</ span > < span class ="o "> .</ span > < span class ="n "> randint</ span > < span class ="p "> (</ span > < span class ="n "> low</ span > < span class ="p "> ,</ span > < span class ="n "> high</ span > < span class ="p "> ,</ span > < span class ="n "> size</ span > < span class ="p "> )</ span >
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< span class ="gh "> Out[49]: </ span > < span class ="go "> </ span >
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- < span class ="go "> array([[ 5 , 10],</ span >
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- < span class ="go "> [10, 6 ]])</ span >
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+ < span class ="go "> array([[ 6 , 10],</ span >
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+ < span class ="go "> [11, 11 ]])</ span >
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</ pre > </ div >
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</ div >
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< p > < code class ="docutils literal notranslate "> < span class ="pre "> choice</ span > </ code > 可以从给定的列表中,以一定概率和方式抽取结果,当不指定概率时为均匀采样,默认抽取方式为有放回抽样:</ p >
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< div class ="highlight-ipython notranslate "> < div class ="highlight "> < pre > < span > </ span > < span class ="gp "> In [50]: </ span > < span class ="n "> my_list</ span > < span class ="o "> =</ span > < span class ="p "> [</ span > < span class ="s1 "> 'a'</ span > < span class ="p "> ,</ span > < span class ="s1 "> 'b'</ span > < span class ="p "> ,</ span > < span class ="s1 "> 'c'</ span > < span class ="p "> ,</ span > < span class ="s1 "> 'd'</ span > < span class ="p "> ]</ span >
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< span class ="gp "> In [51]: </ span > < span class ="n "> np</ span > < span class ="o "> .</ span > < span class ="n "> random</ span > < span class ="o "> .</ span > < span class ="n "> choice</ span > < span class ="p "> (</ span > < span class ="n "> my_list</ span > < span class ="p "> ,</ span > < span class ="mi "> 2</ span > < span class ="p "> ,</ span > < span class ="n "> replace</ span > < span class ="o "> =</ span > < span class ="kc "> False</ span > < span class ="p "> ,</ span > < span class ="n "> p</ span > < span class ="o "> =</ span > < span class ="p "> [</ span > < span class ="mf "> 0.1</ span > < span class ="p "> ,</ span > < span class ="mf "> 0.7</ span > < span class ="p "> ,</ span > < span class ="mf "> 0.1</ span > < span class ="p "> ,</ span > < span class ="mf "> 0.1</ span > < span class ="p "> ])</ span >
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- < span class ="gh "> Out[51]: </ span > < span class ="go "> array(['d ', 'b '], dtype='<U1')</ span >
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+ < span class ="gh "> Out[51]: </ span > < span class ="go "> array(['b ', 'd '], dtype='<U1')</ span >
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< span class ="gp "> In [52]: </ span > < span class ="n "> np</ span > < span class ="o "> .</ span > < span class ="n "> random</ span > < span class ="o "> .</ span > < span class ="n "> choice</ span > < span class ="p "> (</ span > < span class ="n "> my_list</ span > < span class ="p "> ,</ span > < span class ="p "> (</ span > < span class ="mi "> 3</ span > < span class ="p "> ,</ span > < span class ="mi "> 3</ span > < span class ="p "> ))</ span >
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< span class ="gh "> Out[52]: </ span > < span class ="go "> </ span >
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- < span class ="go "> array([['a', 'd ', 'b'],</ span >
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- < span class ="go "> ['b ', 'a', 'b'],</ span >
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- < span class ="go "> ['c', 'b ', 'd ']], dtype='<U1')</ span >
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+ < span class ="go "> array([['a', 'b ', 'b'],</ span >
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+ < span class ="go "> ['a ', 'a', 'b'],</ span >
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+ < span class ="go "> ['c', 'c ', 'b ']], dtype='<U1')</ span >
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</ pre > </ div >
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</ div >
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< p > 当返回的元素个数与原列表相同时,不放回抽样等价于使用 < code class ="docutils literal notranslate "> < span class ="pre "> permutation</ span > </ code > 函数,即打散原列表:</ p >
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< div class ="highlight-ipython notranslate "> < div class ="highlight "> < pre > < span > </ span > < span class ="gp "> In [53]: </ span > < span class ="n "> np</ span > < span class ="o "> .</ span > < span class ="n "> random</ span > < span class ="o "> .</ span > < span class ="n "> permutation</ span > < span class ="p "> (</ span > < span class ="n "> my_list</ span > < span class ="p "> )</ span >
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- < span class ="gh "> Out[53]: </ span > < span class ="go "> array(['b', 'a ', 'c ', 'd '], dtype='<U1')</ span >
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+ < span class ="gh "> Out[53]: </ span > < span class ="go "> array(['b', 'd ', 'a ', 'c '], dtype='<U1')</ span >
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</ pre > </ div >
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</ div >
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< p > 最后,需要提到的是随机种子,它能够固定随机数的输出结果:</ p >
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