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// SERVER-5044 Standard deviation expression operators
var t = db.server5044;
function test(data, popExpected, sampExpected) {
t.drop();
assert.writeOK(t.insert({})); // need one document to ensure we get output
for (var i = 0; i < data.length; i++)
assert.writeOK(t.insert({num: data[i]}));
var res = t.aggregate({
$group: {
_id: 1,
pop: {$stdDevPop: '$num'},
samp: {$stdDevSamp: '$num'},
}
}).next();
if (popExpected === null) {
assert.isnull(res.pop);
} else {
assert.close(res.pop, popExpected, '', 10 /*decimal places*/);
}
if (sampExpected === null) {
assert.isnull(res.samp);
} else {
assert.close(res.samp, sampExpected, '', 10 /*decimal places*/);
}
}
test([], null, null);
test([1], 0, null);
test([1, 1], 0, 0);
test(['a'], null, null);
test([1, 'a'], 0, null);
test([1, 'a', 1], 0, 0);
test([1, 2], .5, Math.sqrt(.5));
test([1, 2, 3], Math.sqrt(2 / 3), 1);
// test from http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Example
test([4, 7, 13, 16], Math.sqrt(22.5), Math.sqrt(30));
test([1e8 + 4, 1e8 + 7, 1e8 + 13, 1e8 + 16], Math.sqrt(22.5), Math.sqrt(30));
test([1e9 + 4, 1e9 + 7, 1e9 + 13, 1e9 + 16], Math.sqrt(22.5), Math.sqrt(30));
test([1e10 + 4, 1e10 + 7, 1e10 + 13, 1e10 + 16], Math.sqrt(22.5), Math.sqrt(30));
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