间接联合排序函数：np.lexsort((scores, ages))
复数直接排序函数：np.sort_complex(c).real
获取array数组的下标：np.where()[0]
通过下标数组返回数组中的元素集：np.take()
注：np.where()的return: tuple((arr_indices, arr_dtype), )
np.where(namesComplexSorted == 'Kity')
返回值：len==1的tuple: (array([1], dtype=int64),) tuple的元素tuple[0]==(arr_indices, arr_dtype)
需要处理后才能传入list中用于后续使用 : val_return[0][0]
np.take(ages, np.where(ages == v))
参数：(数组a, 下标数组）
返回值：数组a中由下标数组所表示的a数组中的元素集合
1）def take(a, indices, axis=None, out=None, mode='raise'):
Take elements from an array along an axis.
2）Help on built-in function where in module numpy.core.multiarray:
where(...)
where(condition, [x, y])
Return elements, either from `x` or `y`, depending on `condition`.code:
# -*- coding: utf-8 -*-
'''
'''
import numpy as np
names = np.array(['Tom','Mike','Jue','Kity','scote'])
scores = np.array([90., 70., 68., 80., 76.])
ages = np.array([29, 23, 20, 22, 27]) # [29 23 20 22 27]
# 联合排序方法1：返回下标index
index_lexsorted = np.lexsort((scores, ages)) # [2 3 1 4 0]
print(index_lexsorted)
names_lexsorted = names[np.lexsort((scores, ages))] # 间接排序（通过a,b等对c排序； 直接排序是通过a对a排序）
print(names_lexsorted) # ['Jue' 'Kity' 'Mike' 'scote' 'Tom']
print('~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~')
# 联合排序方法2: 巧用复数进行联合排序
c = ages + scores * 1j # j要用 1j 表示
# 复数数组排序函数
d = np.sort_complex(c).real # 直接排序，float:[20. 22. 23. 27. 29.] <class 'numpy.ndarray'>
d = d.astype('int64') # int:[20 22 23 27 29] <class 'numpy.ndarray'>
index_names = []
for i, v in enumerate(d):
print(np.where(ages ==v)[0][0], np.take(ages, np.where(ages == v))[0][0])
index_names.append(np.where(ages ==v)[0][0]) # 按照d的元素顺序依次对比，取出ages的下标
namesComplexSorted = names[index_names]
print(namesComplexSorted) # ['Jue' 'Kity' 'Mike' 'scote' 'Tom']
print(np.where(namesComplexSorted == 'Kity')[0][0]) # (array([1], dtype=int64),)
'''
Help on built-in function lexsort in module numpy.core.multiarray:
lexsort(...)
lexsort(keys, axis=-1)
Perform an indirect sort using a sequence of keys.
Given multiple sorting keys, which can be interpreted as columns in a
spreadsheet, lexsort returns an array of integer indices that describes
the sort order by multiple columns. The last key in the sequence is used
for the primary sort order, the second-to-last key for the secondary sort
order, and so on. The keys argument must be a sequence of objects that
can be converted to arrays of the same shape. If a 2D array is provided
for the keys argument, it's rows are interpreted as the sorting keys and
sorting is according to the last row, second last row etc.
Parameters
----------
keys : (k, N) array or tuple containing k (N,)-shaped sequences
The `k` different "columns" to be sorted. The last column (or row if
`keys` is a 2D array) is the primary sort key.
axis : int, optional
Axis to be indirectly sorted. By default, sort over the last axis.
Returns
-------
indices : (N,) ndarray of ints
Array of indices that sort the keys along the specified axis.
'''
'''
def sort_complex(a):
Sort a complex array using the real part first, then the imaginary part.
'''