JoinAcross

JoinAcross[{a1, a2, ...}, {b1, b2, ...}, key] gives a list of associations obtained by joining those pairs of associations ai and bj in which the values associated with key are the same.

• JoinAcross[{a1, a2, ...}, {b1, b2, ...}, {key1, key2, ...}] joins pairs of associations only when the values associated with all keys keyi are the same.
• JoinAcross[{a1, a2, ...}, {b1, b2, ...}, keya -> keyb] joins pairs of associations ai, bj in which the values associated with keya in the ai are the same as those associated with keyb in the bj.
• JoinAcross[alist, blist, keyspec, "joinspec"] uses joinspec to determine when to allow associations that contain missing elements to be generated.

Examples

JoinAcross[{<|"a" -> 1, "b" -> 2|>}, {<|"a" -> 1, "c" -> 3|>}, "a"]

JoinAcross[{<|"x" -> 1|>, <|"x" -> 2|>}, {<|"x" -> 1, "y" -> 10|>}, "x"]

Please visit the official Wolfram Language Reference for more details.