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Is there a better way to iterate over two lists, getting one element from each list for each iterati
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answered Dec 17 '09 at 2:03
Roberto BonvalletRoberto Bonvallet
25.9k55 gold badges3737 silver badges5555 bronze badges
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Element-wise addition of 2 lists?
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371
Use map with operator.add:
>>> from operator import add
>>> list( map(add, ...
Select multiple columns in data.table by their numeric indices
... all just work:
library(data.table)
dt <- data.table(a = 1, b = 2, c = 3)
# select single column by index
dt[, 2]
# b
# 1: 2
# select multiple columns by index
dt[, 2:3]
# b c
# 1: 2 3
# select single column by name
dt[, "a"]
# a
# 1: 1
# select multiple columns by name
dt[, c("a", ...
Extract first item of each sublist
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Using list comprehension:
>>> lst = [['a','b','c'], [1,2,3], ['x','y','z']]
>>> lst2 = [item[0] for item in lst]
>>> lst2
['a', 1, 'x']
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Maximum number of characters using keystrokes A, Ctrl+A, Ctrl+C and Ctrl+V
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43
There's a dynamic programming solution. We start off knowing 0 keys can make us 0 A's. Then we i...
How to select rows with one or more nulls from a pandas DataFrame without listing columns explicitly
I have a dataframe with ~300K rows and ~40 columns.
I want to find out if any rows contain null values - and put these 'null'-rows into a separate dataframe so that I could explore them easily.
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What does the “yield” keyword do?
...ng its items one by one is called iteration:
>>> mylist = [1, 2, 3]
>>> for i in mylist:
... print(i)
1
2
3
mylist is an iterable. When you use a list comprehension, you create a list, and so an iterable:
>>> mylist = [x*x for x in range(3)]
>>> for i in my...
how to concatenate two dictionaries to create a new one in Python? [duplicate]
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Slowest and doesn't work in Python3: concatenate the items and call dict on the resulting list:
$ python -mtimeit -s'd1={1:2,3:4}; d2={5:6,7:9}; d3={10:8,13:22}' \
'd4 = dict(d1.items() + d2.items() + d3.items())'
100000 loops, best of 3: 4.93 usec per loop...
Array slices in C#
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13
Note using Array.Copy performs a lot faster than using LINQ's Take or Skip methods.
– Michael
Jun 23 ...
do N times (declarative syntax)
..., without any library, just native vanilla.
To basically call something() 3 times, use:
[1,2,3].forEach(function(i) {
something();
});
considering the following function:
function something(){ console.log('something') }
The outpout will be
something
something
something
To complete thi...