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I'm looking to import the 4th column of data from a few hundred CSV files that I have stored in various folders. I have been able to import all CSV files from a given directory through use of:

allFiles = Filenames[".csv","/filepath/"]; and list1 = Import[#,"Dataset"]&/@allFiles;

However, I haven't been able to extract the 4th column of data from the lists once the files have been imported. Is there an easier way to do this?

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    – rhermans
    Jun 13, 2018 at 19:12
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1 Answer 1

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TL; DR

Import[#, {"CSV", "Data", All, 4}] &

Import specific columns

Notice in the documentation for Import and for CSV that it explicitly states that you can do

Import["file.csv",{element, subelement1, subelement2], ...}] to import subelements, specifically useful for partial data import.

Mathematica graphics

Example

Example data

data = Table[
   FromDigits[{i , j}]
   , {i, 0, 9}
   , {j, 1, 10}
   ];
TableForm[
 data
 , TableHeadings -> Automatic
 ]

Mathematica graphics

Save to file

Export[
 "Test.CSV"
 , data
 ];

Import

Import["Test.CSV", {"CSV", "Data", All, 4}]
(*{4, 14, 24, 34, 44, 54, 64, 74, 84, 94} *)
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    $\begingroup$ This will also work for the "Dataset" element, which op appeared to want to use. I strongly recommend adding "FillRows" -> True as well especially for "Dataset". Import[#, {"CSV", "Dataset", All, 4}, "FillRows" -> True] & $\endgroup$
    – GenericAccountName
    Jun 13, 2018 at 20:47
  • $\begingroup$ For multiple columns: Import[f, {"CSV", "Data", All, {co1, col2, col3, ...}}] $\endgroup$
    – Dan Oak
    Jun 2, 2021 at 22:17

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