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I have a Dataset of only 1 column to start with, and I want to StringJoin every element there. Got the error message

StringJoin::string: String expected at position 1 in StringJoin[Dataset [<<33>>]].

Here is code to reproduce:

a = {1, 2, 3}
b = Dataset[ToString /@ a]
c = StringJoin[b]

Tried Normal[StringJoin[b]] & Normal[b], neither worked.

Thanks in advance.

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  • $\begingroup$ StringJoin[(# & /@ Normal@b)] is this what you're looking for? Edit: Commented before seeing WReach's answer. It's a really nice way of doing this! :) $\endgroup$
    – Vahagn Tumanyan
    Commented May 4, 2017 at 16:57
  • $\begingroup$ This solution works, thanks! $\endgroup$
    – user1470393
    Commented May 4, 2017 at 17:14

2 Answers 2

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StringJoin is not one of the functions that support a dataset argument. We can, however, use StringJoin as a query operator:

b[StringJoin]

(* "123" *)

We can see the functions which do accept a dataset argument by inspecting the output of:

Needs["GeneralUtilities`"]
PrintDefinitions[Dataset]

PrintDefinitions screenshot

The list is quite a bit longer than will fit in a screenshot.

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In:

a = {1, 2, 3};
b = Dataset[ToString /@ a];

b[StringJoin, All] (*Method 1, apply StringJoin to the contents of all columns/a specific column*)
StringJoin @@ b (*Method 2, replace Dataset head with StringJoin*)

Out:

"123"
"123"
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