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Time complexity of Sieve of Eratosthenes algorithm
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Your n/2 + n/3 + n/5 + … n/97 is not O(n), because the number of terms is not constant. [Edit after your edit: O(n2) is too loose an upper bound.] A loose upper-bound is n(1+1/2+1/3+1/4+1/5+1/6+…1/n) (sum of reciprocals of all n...
Get distance between two points in canvas
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211
You can do it with pythagoras theorem
If you have two points (x1, y1) and (x2, y2)
then you c...
How to format time since xxx e.g. “4 minutes ago” similar to Stack Exchange sites
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25 Answers
25
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Is there an R function for finding the index of an element in a vector?
...rks on vectors :
x <- sample(1:10)
x
# [1] 4 5 9 3 8 1 6 10 7 2
match(c(4,8),x)
# [1] 1 5
match only returns the first encounter of a match, as you requested. It returns the position in the second argument of the values in the first argument.
For multiple matching, %in% is the way to...
Installing Numpy on 64bit Windows 7 with Python 2.7.3 [closed]
...nstaller for Numpy is for Numpy version 1.3.0 which only works with Python 2.6
6 Answers
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Why does ~True result in -2?
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240
int(True) is 1.
1 is:
00000001
and ~1 is:
11111110
Which is -2 in Two's complement1
1 ...
How do I list all versions of a gem available at a remote site?
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205
Well, it was easier than I thought (well, not really, let's say as easy as it should be):
gem...
warning: [options] bootstrap class path not set in conjunction with -source 1.5
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102
From a blog post:
To use javac from JDK N to cross-compiler to an older platform version, th...
Pass a data.frame column name to a function
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You can just use the column name directly:
df <- data.frame(A=1:10, B=2:11, C=3:12)
fun1 <- function(x, column){
max(x[,column])
}
fun1(df, "B")
fun1(df, c("B","A"))
There's no need to use substitute, eval, etc.
You can even pass the desired function as a parameter:
fun1 <- function...
python numpy machine epsilon
...for a given float type is to use np.finfo():
print(np.finfo(float).eps)
# 2.22044604925e-16
print(np.finfo(np.float32).eps)
# 1.19209e-07
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