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Difference between declaring variables before or in loop?
I have always wondered if, in general, declaring a throw-away variable before a loop, as opposed to repeatedly inside the loop, makes any (performance) difference?
A (quite pointless) example in Java:
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Get records with max value for each group of grouped SQL results
... a super-simple way to do this in mysql:
select *
from (select * from mytable order by `Group`, age desc, Person) x
group by `Group`
This works because in mysql you're allowed to not aggregate non-group-by columns, in which case mysql just returns the first row. The solution is to first order the ...
How to implement a queue with three stacks?
I came across this question in an algorithms book ( Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne).
5 Answ...
Append an object to a list in R in amortized constant time, O(1)?
If I have some R list mylist , you can append an item obj to it like so:
17 Answers
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Shuffling a list of objects
I have a list of objects and I want to shuffle them. I thought I could use the random.shuffle method, but this seems to fail when the list is of objects. Is there a method for shuffling objects or another way around this?
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Does JavaScript have “Short-circuit” evaluation?
...rcuit" evaluation.
if (true == true || foo.foo){
// Passes, no errors because foo isn't defined.
}
Live DEMO
if (false && foo.foo){
// Passes, no errors because foo isn't defined.
}
Live DEMO
share
...
pandas three-way joining multiple dataframes on columns
...g) names of people, while all the other columns in each dataframe are attributes of that person.
10 Answers
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Changing java platform on which netbeans runs
I am using Netbeans 6.7. I had first installed Java 1.5 before installing Netbeans. When i installed Netbeans it took Java 1.5 as the default version. Then i installed Java 1.6 on my machine. I need to change the default JDK of my netbeans to 1.6 not only to a specific project but to the whole Netbe...
How to get all subsets of a set? (powerset)
...e has exactly a powerset recipe for this:
from itertools import chain, combinations
def powerset(iterable):
"powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)"
s = list(iterable)
return chain.from_iterable(combinations(s, r) for r in range(len(s)+1))
Output:
>&...
Better way to sum a property value in an array
...erCollection extends Array {
sum(key) {
return this.reduce((a, b) => a + (b[key] || 0), 0);
}
}
const traveler = new TravellerCollection(...[
{ description: 'Senior', Amount: 50},
{ description: 'Senior', Amount: 50},
{ description: 'Adult', Amount: 75},
{ desc...