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Here is what I have tried first.

Thread[f["x", {"1", "2"}]]

{f["x", "1"], f["x", "2"]}

But the weirdest thing happened when I substituted StringJoin for f

Thread[StringJoin["x", {"1", "2"}]]

"x12"

I thought it would be like this below

{"x1","x2"}

Is there anyone who can explain this?

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    $\begingroup$ Why use Thread for this? Table["x"<>n, {n, {"1","2"}}] or "x"<>#&/@{"1","2"} seem like more straightforward ways to get this result. $\endgroup$ – Jason B. Aug 11 '20 at 1:51
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Thread >> Possible Issues:

  • "Thread evaluates the whole expression before threading"

Wrap StringJoin with Unevaluated to prevent evaluation of StringJoin before Thread gets to work:

Thread[Unevaluated @ StringJoin["x", {"1", "2"}]]
{"x1", "x2"}

Alternatively, you can use

Thread[foo["x", {"1", "2"}]] /. foo -> StringJoin
{"x1", "x2"}
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