numpy學習筆記之隨機採樣函數

numpy的隨機採樣函數

• np.random.choice(a, size=None,replace=None, p=None)

  • 功能：Generates a random sample from a given 1-D array

  • 常見的隨機採樣用法如下：

    import random 
    # 從0到99的列表中隨機生成10個樣本
    out1 = random.sample(range(100),10) # 方法1
    
    # If a is an int, the random sample is generated as if a was np.arange(n)
    out2 = np.random.choice(100,10) # 方法2 
    # 結果可能會出現相同的數，通過set()進行去重,
    out = set(out2)
    
    # 從input數組或者列表中隨機生成一個樣本
    input = [1,3,6,8]
    output = np.random.choice(input)
    
    # 從input數組或列表中以一定的概率生成樣本
    # 選擇元素8的概率最大爲0.4
    input = [1,3,6,8]
    output = np.random.choice(input,p=[0.1,0.2,0.3,0.4])
    
    aa_milne_arr = ['pooh', 'rabbit', 'piglet', 'Christopher']
    np.random.choice(aa_milne_arr, 5, p=[0.5, 0.1, 0.1, 0.3])
     #array(['pooh', 'pooh', 'pooh', 'Christopher', 'piglet'], dtype='|S11')
    

  • np.random.choice的API 如下：

    choice(a, size=None, replace=True, p=None)
        Parameters
        -----------
        a : 1-D array-like or int
            If an ndarray, a random sample is generated from its elements.
            If an int, the random sample is generated as if a was np.arange(n)
        size : int or tuple of ints, optional
            Output shape.  If the given shape is, e.g., ``(m, n, k)``, then
            ``m * n * k`` samples are drawn.  Default is None, in which case a
            single value is returned.
        replace : boolean, optional
            Whether the sample is with or without replacement
        p : 1-D array-like, optional
            The probabilities associated with each entry in a.
            If not given the sample assumes a uniform distribution over all
            entries in a.
    
        Returns
      	  samples : 1-D ndarray, shape (size,)
      	      The generated random samples
    

  See Also

  randint, shuffle, permutation

  • np.random.randint(0,10)

    • 功能：隨機從0到10之間選取一個數

    • randint(low, high=None, size=None, dtype='l')

    • Return random integers from low (inclusive) to high (exclusive)

  • np.random.shuffle (array)

    • 功能：隨機對給定數組或者列表亂序，默認是axis=0
    • 返回的結果就是給定數組本身，只不過順序被打亂

  • np.random.permutation(array)

    • 功能：重新對給定數組或者列表排序，如何是多維數組，則沿着first axis重新排列，
    • 返回的重新排列後的數組