I want to sum every element of x[i] except when i = j. For example: j=10 I = 1:30 sum(x[i] for i in I) #here I want to sum every element but j.

There’s always the simple sum(x)-x[j]

Unless “the one” element is problematic, e.g., it’s NaN or much larger than the others, summing everything and then subtracting one element is probably the fastest method by far. If the element is problematic, you could set it to 0 before summing, and then set it back afterwards. a = randn(1000) @…

This is what I needed, thanks. [image] greg_plowman: sum(x[i] for i in I if i != j)

Thank you for the explanation. I needed the second one. [image] baggepinnen: @btime sum($a[i] for i in eachindex($a) if i != 100)

Another direct approach, much faster than the generator: @btime sum(i -> i == 100 ? 0. : @inbounds($a[i]), eachindex($a)) # 182.628 ns (0 allocations: 0 bytes)

How to sum every element but one

General Usage

greg_plowman November 8, 2020, 7:25am 3

sum(x[i] for i in I if i != j)

Is there a nice way to specify sums or products with excluded indices?

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How to sum every element but one

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