Export, Import and extra curly brackets?

Question

list= {{}, {200, 200, 200}, {}, {201, 201}};
Export["list.csv", {list}, "csv"]
data = Import["lnumber.csv", "csv"];

The result of this export and import is an extra curly bracket.

 (* data -> {{{}, {200, 200, 200}, {}, {201, 201}}} *)

(Note:without " "in output).

However, I want {200, 200, 200, 201, 201}.

Flatten[data] doesn't give the desired result. One way to overcome the problem is to Flatten[list] before exporting.

But, I want to Flatten[data] to get the desired result.

Answer 1

Your usage of "CSV" export is incorrect: exported list of numbers should be a 2D numerical array, while with {list} you supply a 3D array. With correct "CSV" format you can use advanced Import options:

list = {{}, {200, 200, 200}, {}, {201, 201}};
Export["list.csv", list, "CSV"];
data = Import["list.csv", "Table", "FieldSeparators" -> ","]

{{}, {200, 200, 200}, {}, {201, 201}}

Flatten[%]

{200, 200, 200, 201, 201}

Note that in version 8.0.4 the following does the job even better :

Import["list.csv", "CSV", "IgnoreEmptyLines" -> True]

{{200, 200, 200}, {201, 201}}

For some reason in versions 11.2.0 and 11.3.0 the option "IgnoreEmptyLines" -> True does nothing, what looks like a bug.

Answer 2

However, I want {200, 200, 200, 201, 201}

Try

 data=Import["list.csv","CSV"]
 Flatten@ToExpression[data]

Answer 3

A few points. First, you are not importing the same file that you're exporting. Is that intentional?

Secondly, the extra bracket is due to the extra bracket in the Export line:

Export["list.csv", {list}, "csv"]

Is not exactly the same as:

Export["list.csv", list, "csv"]

The latter exports list in .csv format, while the former exports a list containing list in .csv format. If you make that change, the extra bracket will disappear.

With that change, it is worth noting that the empty lists are imported as {""} (check FullForm[data] to see for yourself). This will result in spurious empty spaces showing up in Flatten[data]. DeleteCases can be used to clean it up:

DeleteCases[Flatten[data],""]