我如何有效地获得一个NumPy数组中每个唯一值的频率计数?
>>> x = np.array([1,1,1,2,2,2,5,25,1,1])
>>> freq_count(x)
[(1, 5), (2, 3), (5, 1), (25, 1)]
我如何有效地获得一个NumPy数组中每个唯一值的频率计数?
>>> x = np.array([1,1,1,2,2,2,5,25,1,1])
>>> freq_count(x)
[(1, 5), (2, 3), (5, 1), (25, 1)]
当前回答
看看np.bincount:
http://docs.scipy.org/doc/numpy/reference/generated/numpy.bincount.html
import numpy as np
x = np.array([1,1,1,2,2,2,5,25,1,1])
y = np.bincount(x)
ii = np.nonzero(y)[0]
然后:
zip(ii,y[ii])
# [(1, 5), (2, 3), (5, 1), (25, 1)]
or:
np.vstack((ii,y[ii])).T
# array([[ 1, 5],
[ 2, 3],
[ 5, 1],
[25, 1]])
或者你想结合计数和唯一值。
其他回答
import pandas as pd
import numpy as np
print(pd.Series(name_of_array).value_counts())
Most of simple problems get complicated because simple functionality like order() in R that gives a statistical result in both and descending order is missing in various python libraries. But if we devise our thinking that all such statistical ordering and parameters in python are easily found in pandas, we can can result sooner than looking in 100 different places. Also, development of R and pandas go hand-in-hand because they were created for same purpose. To solve this problem I use following code that gets me by anywhere:
unique, counts = np.unique(x, return_counts=True)
d = {'unique':unique, 'counts':count} # pass the list to a dictionary
df = pd.DataFrame(d) #dictionary object can be easily passed to make a dataframe
df.sort_values(by = 'count', ascending=False, inplace = True)
df = df.reset_index(drop=True) #optional only if you want to use it further
多维频率计数,即计数数组。
>>> print(color_array )
array([[255, 128, 128],
[255, 128, 128],
[255, 128, 128],
...,
[255, 128, 128],
[255, 128, 128],
[255, 128, 128]], dtype=uint8)
>>> np.unique(color_array,return_counts=True,axis=0)
(array([[ 60, 151, 161],
[ 60, 155, 162],
[ 60, 159, 163],
[ 61, 143, 162],
[ 61, 147, 162],
[ 61, 162, 163],
[ 62, 166, 164],
[ 63, 137, 162],
[ 63, 169, 164],
array([ 1, 2, 2, 1, 4, 1, 1, 2,
3, 1, 1, 1, 2, 5, 2, 2,
898, 1, 1,
像这样的东西应该做到:
#create 100 random numbers
arr = numpy.random.random_integers(0,50,100)
#create a dictionary of the unique values
d = dict([(i,0) for i in numpy.unique(arr)])
for number in arr:
d[j]+=1 #increment when that value is found
另外,之前的这篇关于有效计算独特元素的文章似乎与您的问题非常相似,除非我遗漏了什么。
这是迄今为止最通用和性能最好的解决方案;很惊讶它还没有发布。
import numpy as np
def unique_count(a):
unique, inverse = np.unique(a, return_inverse=True)
count = np.zeros(len(unique), np.int)
np.add.at(count, inverse, 1)
return np.vstack(( unique, count)).T
print unique_count(np.random.randint(-10,10,100))
与目前接受的答案不同,它适用于任何可排序的数据类型(不仅仅是正整数),并且具有最佳性能;唯一重要的开销是np.unique所做的排序。