# Slow JoinAcross performance

Bug introduced in 10.3

I am using JoinAcross to combine two datasets, where the key is an Integer.

L = Get["https://dl.dropboxusercontent.com/u/557392/permalink/StackExchange/mathematica/107732/L.m"];

JoinAcross[L, R, "A", "Inner"]


The Dataset rendition of these associations is

For L:

For R:

Though this takes a couple of seconds in KNIME and/or GNU R, it takes an hour or more in Mathematica 10.3.1 on GNU/Linux.

What can I do to speed this operation up?

• Ask Konstantin at WRI, he wrote that I believe. – M.R. Feb 19 '16 at 2:09
• 4.2 seconds, v10.1/Windows . Similar on my linux box. – george2079 Feb 19 '16 at 22:10
• 3575.66 seconds, v10.3.1/Windows – Alexey Golyshev Feb 20 '16 at 14:11
• 3.0 seconds v10.2/Mac. I guess we've bracketed it to a change between 10.2 and 10.3. Thanks everyone, I have contacted Wolfram Support. – Eric Brown Feb 22 '16 at 14:14
• This is a thousand-fold slowdown. I think the bugs tag was warranted. – Szabolcs Mar 2 '16 at 18:08