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Which SQL query is faster? Filter on Join criteria or Where clause?
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answered Mar 24 '10 at 17:40
QuassnoiQuassnoi
369k8181 gold badges571571 silver badges582582 bronze badges
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Remove empty elements from an array in Javascript
...xample, if you want to remove null or undefined values:
var array = [0, 1, null, 2, "", 3, undefined, 3,,,,,, 4,, 4,, 5,, 6,,,,];
var filtered = array.filter(function (el) {
return el != null;
});
console.log(filtered);
It will depend on what you consider to be "empty" for exa...
Append value to empty vector in R?
...et.seed(21)
values <- sample(letters, 1e4, TRUE)
vector <- character(0)
# slow
system.time( for (i in 1:length(values)) vector[i] <- values[i] )
# user system elapsed
# 0.340 0.000 0.343
vector <- character(length(values))
# fast(er)
system.time( for (i in 1:length(values)) vec...
Is there an equivalent of 'which' on the Windows command line?
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Windows Server 2003 and later (i.e. anything after Windows XP 32 bit) provide the where.exe program which does some of what which does, though it matches all types of files, not just executable commands. (It does not match built-in shell co...
Convert column classes in data.table
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105
For a single column:
dtnew <- dt[, Quarter:=as.character(Quarter)]
str(dtnew)
Classes ‘d...
Difference between MEAN.js and MEAN.io
...response!
– CMPSoares
Apr 22 '14 at 0:08
7
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Principal component analysis in Python
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edited Sep 3 '10 at 11:40
nikow
19.6k66 gold badges4242 silver badges6969 bronze badges
answe...
Frequency table for a single variable
...es = pandas.Series([1,2,2,3,3,3, "fred", 1.8, 1.8])
>>> my_series
0 1
1 2
2 2
3 3
4 3
5 3
6 fred
7 1.8
8 1.8
>>> counts = my_series.value_counts()
>>> counts
3 3
2 2
1.8 2
fred 1
1 1
>>> len(c...
How to crop an image in OpenCV using Python
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crop_img = img[y:y+h, x:x+w]
cv2.imshow("cropped", crop_img)
cv2.waitKey(0)
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Git Extensions: Win32 error 487: Couldn't reserve space for cygwin's heap, Win32 error 0
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Dyin
6,91066 gold badges3939 silver badges5959 bronze badges
answered Aug 29 '13 at 6:03
Greg HewgillGreg Hewg...