Getting the variance of a vector of long doubles

Question

I'm trying to calculate the variance of a vector of long doubles. I've tried implementing other code I've seen, but it doesn't return the correct value.

long double variance = 0;
for (int x = 0; x < (v.size() - 1); x++) {
    variance += (v.at(x) - mean) * (v.at(x) - mean);
}
variance /= v.size();

For example, if my vector is {1,2,3,4,5}, the above code gives me 2.25. To my understanding the correct answer is 2.

Any help is appreciated, I'm not sure what I'm missing.

Try not to use explicit for loops, try to use STL algorithm like transform. Exact solution to your problem at https://stackoverflow.com/a/12405793/171755 — jbp, Mar 15 '18 at 00:59

score 3 · Accepted Answer · answered Mar 15 '18 at 00:35

3

x < (v.size() - 1)? This skips the last element. Use <= or omit the - 1.

The index of the element is v.size() - 1, and since x must be less than that, the loop breaks before the last element is processed.

answered Mar 15 '18 at 00:35

eesiraed

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Oh. That was a dumb mistake. – Owl Mar 15 '18 at 00:42

Getting the variance of a vector of long doubles

1 Answers1