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How to convert a data frame column to numeric type?
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18 Answers
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App Inventor 2 数学代码块 · App Inventor 2 中文网
...最多的元素 (mode)
案例：指定将二进制的某一位(Bit)改为1
案例：指定将二进制的某一位(Bit)改为0
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等于 ( = )
不等于 ( ≠ )
大于 ( > )
大于等于 ( ≥ )
小于 ( < )
小于等于 ( ≤ )
加 (...
How to reorder data.table columns (without copying)
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185
Use setcolorder():
library(data.table)
x <- data.table(a = 1:3, b = 3:1, c = runif(3))
x
#...
How to add new item to hash
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Create the hash:
hash = {:item1 => 1}
Add a new item to it:
hash[:item2] = 2
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How to count the number of true elements in a NumPy bool array
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>>> import numpy as np
>>> boolarr = np.array([[0, 0, 1], [1, 0, 1], [1, 0, 1]], dtype=np.bool)
>>> boolarr
array([[False, False, True],
[ True, False, True],
[ True, False, True]], dtype=bool)
>>> np.sum(boolarr)
5
Of course, that is a bool...
SQL query return data from multiple tables
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Part 1 - Joins and Unions
This answer covers:
Part 1
Joining two or more tables using an inner join (See the wikipedia entry for additional info)
How to use a union query
Left and Right Outer Joins (this stackOverflow answer ...
Python integer division yields float
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answered Aug 15 '09 at 21:51
Brandon E TaylorBrandon E Taylor
23.1k66 gold badges4343 silver badges6868 bronze badges
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Syntax for creating a two-dimensional array
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Selecting with complex criteria from pandas.DataFrame
...; from random import randint
>>> df = pd.DataFrame({'A': [randint(1, 9) for x in range(10)],
'B': [randint(1, 9)*10 for x in range(10)],
'C': [randint(1, 9)*100 for x in range(10)]})
>>> df
A B C
0 9 40 300
1 9 70 700
2 5 70 90...
Grep regex NOT containing string
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351
grep matches, grep -v does the inverse. If you need to "match A but not B" you usually use pipes...