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Python - Create a list with initial capacity
...
def doAppend( size=10000 ):
result = []
for i in range(size):
message= "some unique object %d" % ( i, )
result.append(message)
return result
def doAllocate( size=10000 ):
result=size*[None]
for i in range(siz...
How is a CRC32 checksum calculated?
...e polynomial for CRC32 is:
x32 + x26 + x23 + x22 + x16 + x12 + x11 + x10 + x8 + x7 + x5 + x4 + x2 + x + 1
Wikipedia
CRC calculation
Or in hex and binary:
0x 01 04 C1 1D B7
1 0000 0100 1100 0001 0001 1101 1011 0111
The highest term (x32) is usually not explicitly written, so it can i...
How to swap two variables in JavaScript
...swap the values of two variables.
Given variables a and b:
b = [a, a = b][0];
Demonstration below:
var a=1,
b=2,
output=document.getElementById('output');
output.innerHTML="<p>Original: "+a+", "+b+"</p>";
b = [a, a = b][0];
output.innerHTML+="<p>Swapped: ...
Changing iframe src with Javascript
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answered Sep 16 '10 at 19:43
PekkaPekka
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How to format a Java string with leading zero?
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In case you have to do it without the help of a library:
("00000000" + "Apple").substring("Apple".length())
(Works, as long as your String isn't longer than 8 chars.)
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impro...
wkhtmltopdf: cannot connect to X server
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206
or try this (from http://drupal.org/node/870058)
Download wkhtmltopdf. Or better install it w...
Case preserving substitute in Vim
...toMark Lodato
37.4k55 gold badges3737 silver badges3030 bronze badges
16
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How to find index of list item in Swift?
... // 2
find(arr, "d") // nil
Update for Swift 2.0:
The old find function is not supported any more with Swift 2.0!
With Swift 2.0, Array gains the ability to find the index of an element using a function defined in an extension of CollectionType (which Array implements):...
Ternary operator is twice as slow as an if-else block?
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10 Answers
10
Active
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Group by multiple columns in dplyr, using string vector input
...
data = data.frame(
asihckhdoydkhxiydfgfTgdsx = sample(LETTERS[1:3], 100, replace=TRUE),
a30mvxigxkghc5cdsvxvyv0ja = sample(LETTERS[1:3], 100, replace=TRUE),
value = rnorm(100)
)
# get the columns we want to average within
columns = names(data)[-3]
library(dplyr)
df1 <- data %>%...