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What is the “N+1 selects problem” in ORM (Object-Relational Mapping)?
The "N+1 selects problem" is generally stated as a problem in Object-Relational mapping (ORM) discussions, and I understand that it has something to do with having to make a lot of database queries for something that seems simple in the object world.
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Emulate ggplot2 default color palette
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It is just equally spaced hues around the color wheel, starting from 15:
gg_color_hue <- function(n) {
hues = seq(15, 375, length = n + 1)
hcl(h = hues, l = 65, c = 100)[1:n]
}
For example:
n = 4
cols = gg_color_hue(n)
dev.new(width = 4, height = 4)
plot(1:n, pch = 16, cex = 2, col...
Plot a legend outside of the plotting area in base graphics?
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10 Answers
10
Active
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Convert column classes in data.table
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105
For a single column:
dtnew <- dt[, Quarter:=as.character(Quarter)]
str(dtnew)
Classes ‘...
How to sort an array in descending order in Ruby
... Here's what I found out:
#!/usr/bin/ruby
require 'benchmark'
ary = []
1000.times {
ary << {:bar => rand(1000)}
}
n = 500
Benchmark.bm(20) do |x|
x.report("sort") { n.times { ary.sort{ |a,b| b[:bar] <=> a[:bar] } } }
x.report("sort reverse") { n.times ...
Why is SSE scalar sqrt(x) slower than rsqrt(x) * x?
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216
sqrtss gives a correctly rounded result. rsqrtss gives an approximation to the reciprocal, acc...
Does assignment with a comma work?
Why does aaa = 1,2,3 work and set the value of aaa to 1 ?
4 Answers
4
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Slicing of a NumPy 2d array, or how do I extract an mxm submatrix from an nxn array (n>m)?
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As Sven mentioned, x[[[0],[2]],[1,3]] will give back the 0 and 2 rows that match with the 1 and 3 columns while x[[0,2],[1,3]] will return the values x[0,1] and x[2,3] in an array.
There is a helpful function for doing the first example I gave, numpy.ix_....