How to change a key's value of association?

I want to write a pure function to change the key's value of an association, it must return the new association, so it can be mapped to a table of associations.

The AssociateTo can change key's value of an association, but it seems not working. I don't know why, perhaps because it is not a pure function?

So if I have a pure function doing the same thing, this job can be done very well.

Can you help me? Thanks!

• Use Append. AssociateTo is for changing the value of a variable. You have no variables. – Szabolcs Mar 2 '17 at 8:07
• In general case Merge[Last], in even more general case 102466, but here, in addition to what Szabolcs said, you can <|#, "key"->value|>&/@data – Kuba Mar 2 '17 at 8:13
• Thank you. <|#, "key"->value|> works well. – cmal Mar 2 '17 at 8:15
• closely related: 74165, 137455 – Kuba Mar 2 '17 at 8:29