Merging two associations

Question

I have two associations:

assoc1= <|"HD 164019" -> {"1.05", "1.37", "A"}, "* 63 Oph" -> {"-0.77", "0.40", "A"}, "HD 168941" -> {"-3.76", "1.38", "A"}, "* 9 Sgr" -> {"0.49", "0.40", "A"}, "HD 165052" -> {"0.15", "0.63", "A"}, "* zet Oph" -> {"8.91", "0.20", "A"}, "HD 165921" -> {"2.18", "0.67", "A"}, "HD 163800" -> {"-1.01", "0.66", "A"}, "HD 163892" -> {"-0.50", "0.69", "A"}, "HD 313846" -> {"-0.46", "1.79", "A"},.....

assoc2 = <|" HD 164019 " -> {"O9.5IV"}, " * 63 Oph " -> {"O8II"}, " HD 168941 " -> {"O9.5IV"}, " HD 164536 " -> {"O7.5V"}, " NAME Her 36 " -> {"O7:V"}, " * 9 Sgr " -> {"O4V((f))z"}, " HD 164816 " -> {"O9.5V+B0V"}, " HD 165052 " -> {"O7Vz+O7.5Vz"}, " * zet Oph " -> {"O9.2IV"}, " HD 165246 " -> {"O8V"}, " HD 165921 " -> {"O7V+O9V"}, " HD 164492A " -> {"O7.5Vz"}, " HD 163800 " -> {"O7.5III(f)"}, " HD 163892 " -> {"B0.5/B1Ib"}, " HD 313846 " -> {"WN9h"},...

I want to merge them into a single association like this:

assoc3 = " HD 164019 " -> {"O9.5IV","1.05", "1.37", "A"}, " * 63 Oph " -> {"O8II","-0.77", "0.40", "A"}...

I tried

assoc3 = Merge[Join{assoc1, assoc2}, Identity]

but it didn't work.

Has anybody any suggestion on how implement it?

Answer 1

The keys in the two associations must be the same. This is not the case in your example. Restricting things to just the first two elements in your associations (enough to make the point), you have

assoc1 = 
   <|"HD 164019" -> {"1.05", "1.37", "A"}, "* 63 Oph" -> {"-0.77", "0.40", "A"}|>;
assoc2 = <|" HD 164019 " -> {"O9.5IV"}, " * 63 Oph " -> {"O8II"}|>;

The extra spaces in the keys of assoc2 are bad and must be removed.

assoc2 = <|"HD 164019" -> {"O9.5IV"}, "* 63 Oph" -> {"O8II"}|>;

Now your problem can be solved with

Merge[{assoc2, assoc1}, Flatten]

<|"HD 164019" -> {"O9.5IV", "1.05", "1.37", "A"}, 
  "* 63 Oph" -> {"O8II", "-0.77", "0.40", "A"}|>

Note that to get the ordering you show in your example, you must give Merge,{assoc2, assoc1}; the order matters.