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Fastest way to replace NAs in a large data.table
...e a large data.table , with many missing values scattered throughout its ~200k rows and 200 columns. I would like to re code those NA values to zeros as efficiently as possible.
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Scala: Nil vs List()
...intln (Nil equals List())
true
scala> System.identityHashCode(Nil)
374527572
scala> System.identityHashCode(List())
374527572
Nil is more idiomatic and can be preferred in most cases.
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Pad a string with leading zeros so it's 3 characters long in SQL Server 2008
...ring that is up to 3 characters long when it's first created in SQL Server 2008 R2.
17 Answers
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How to convert an enum type variable to a string?
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Is R's apply family more than syntactic sugar?
...ntly different performance:
> fibo <- function(n) {
+ if ( n < 2 ) n
+ else fibo(n-1) + fibo(n-2)
+ }
> system.time(for(i in 0:26) fibo(i))
user system elapsed
7.48 0.00 7.52
> system.time(sapply(0:26, fibo))
user system elapsed
7.50 0.00 7.54
> s...
Python: Continuing to next iteration in outer loop
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72
for i in ...:
for j in ...:
for k in ...:
if something:
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Is unsigned integer subtraction defined behavior?
...t can be
represented by the resulting type.
(ISO/IEC 9899:1999 (E) §6.2.5/9)
As you can see, (unsigned)0 - (unsigned)1 equals -1 modulo UINT_MAX+1, or in other words, UINT_MAX.
Note that although it does say "A computation involving unsigned operands can never overflow", which might lead ...
SQL query for today's date minus two months
... select all the records in a table where their date of entry is older then 2 months.
5 Answers
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John Carmack's Unusual Fast Inverse Square Root (Quake III)
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answered Aug 28 '09 at 21:52
RushyoRushyo
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fork() branches more than expected?
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245
The fork() primitive often stretches the imagination. Until you get a feel for it, you should...