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Boolean operators && and ||
...an return a vector, like this:
((-2:2) >= 0) & ((-2:2) <= 0)
# [1] FALSE FALSE TRUE FALSE FALSE
The longer form evaluates left to right examining only the first element of each vector, so the above gives
((-2:2) >= 0) && ((-2:2) <= 0)
# [1] FALSE
As the help page says...
Unique (non-repeating) random numbers in O(1)?
I'd like to generate unique random numbers between 0 and 1000 that never repeat (i.e. 6 doesn't show up twice), but that doesn't resort to something like an O(N) search of previous values to do it. Is this possible?
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Python assigning multiple variables to same value? list behavior
... and Chris Wallace have a hot dog. If you change the first element of a to 1, the first elements of b and c are 1.
If you want to know if two names are naming the same object, use the is operator:
>>> a=b=c=[0,3,5]
>>> a is b
True
You then ask:
what is different from this...
Aggregate / summarize multiple variables per group (e.g. sum, mean)
...he reshape2 package for this task:
require(reshape2)
df_melt <- melt(df1, id = c("date", "year", "month"))
dcast(df_melt, year + month ~ variable, sum)
# year month x1 x2
1 2000 1 -80.83405 -224.9540159
2 2000 2 -223.76331 -288.2418017
3 2000 3 -188.83930 -481....
How to scale down a range of numbers with a known min and max value
...anel. I want the height and width of each ellipse to be in a range of say 1-30. I have methods that find the minimum and maximum values from my data set, but I won't have the min and max until runtime. Is there an easy way to do this?
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What is the smallest possible valid PDF?
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198
This is an interesting problem. Taking it by the book, you can start off with this:
%PDF-1.0...
Get index of array element faster than O(n)
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118
Convert the array into a hash. Then look for the key.
array = ['a', 'b', 'c']
hash = Hash[arr...
Disable migrations when running unit tests in Django 1.7
Django 1.7 introduced database migrations .
7 Answers
7
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