Efficient image Import

I have several sets of 20 images I need to import.

Each time they have different categories.

"Name"<>"Cat"<>"No"

Electric B 1 for example.

I need to create lists that contain the images for those different categories.

As of now this is what i am doing :

importOne[set_, cat_, num_] := 
 ImageResize[
  Import[FileNameJoin[{NotebookDirectory[], set, 
         set <> cat <> ToString[num] <> ".png"}]], 128]




ElectricB = importOne["Electric", "B", #] & /@ Range[6];
ElectricC = importOne["Electric", "C", #] & /@ Range[5];
ElectricN = importOne["Electric", "N", #] & /@ Range[5];
ElectricE = importOne["Electric", "E", #] & /@ Range[4];

And then, thanks to previous question/answers :

What would be a more efficient mean to import automatically for different sets ?

As of now I need to repeat this operation for each set.

Answer

Make your filenames unambiguously parsable, e.g. by consistently using some delimeters like underscores or something. A typical file name can look like "Electric_B_3.png". EDIT If you have no control over the file names, use string patterns as described by other answers, but in the long-term you may benefit from creating your own robust naming scheme END EDIT

Then write a function that would parse a single file name, something like:

fileNameParse[fname_String, delim_String: "_"] :=
   StringSplit[FileBaseName[fname], delim]

Then, Map it on FileNames["*.png", {your-dir}].

Finally, apply your importOne on the level one:

importOne@@@Map[fileNameParse, FileNames["*.png", {your-dir}]]

Since you have the result of Map available as well, you can regroup them any way you want. You can, for example, Map a function {#, importOne@@#}&, rather than just using importOne@@@.... Then, you could use GatherBy or any other means to regroup and collect your images according to the parts of their filenames.

EDIT

Here is a self-contained example ( I use text files, but this doesn't matter):

ClearAll[fileNameParse, fileNameMake, importOne, $dir];
fileNameParse[fname_String, delim_String: "_"] :=
    StringSplit[FileBaseName[fname], delim];

fileNameMake[pieces_List, delim_String: "_", ext_String: ".txt"] :=
    StringJoin[Append[Riffle[pieces, "_"], ".txt"]];


importOne[set_, cat_, num_, dir_: $dir] :=
    Import[FileNameJoin[{dir, fileNameMake[{set, cat, num}]}]];

We now create a temporary directory:

$dir = FileNameJoin[{$TemporaryDirectory, "ImportTest"}];
If[! FileExistsQ[$dir], CreateDirectory[$dir]];

Create sample files:

MapIndexed[

   Export[#, "Test" <> ToString[#2], "Text"] &,
   Flatten[
     Outer[
       FileNameJoin[{$dir, fileNameMake[{##}]}] &,
       {"Electric"}, {"A", "B", "C"}, {"1", "2", "3"}
     ]]];

import them:

imported = Map[{#, importOne @@ #} &,  fileNameParse /@ FileNames["*.txt", {$dir}]]


(* 
  ==>

     {{{"Electric", "A", "1"},  "Test{1}"}, {{"Electric", "A", "2"}, "Test{2}"}, 
      {{"Electric", "A", "3"},  "Test{3}"}, {{"Electric", "B", "1"}, "Test{4}"}, 
      {{"Electric", "B", "2"},  "Test{5}"}, {{"Electric", "B", "3"},  "Test{6}"}, 
      {{"Electric", "C", "1"},  "Test{7}"}, {{"Electric", "C", "2"},  "Test{8}"}, 
      {{"Electric", "C", "3"}, "Test{9}"}
      }
*)

You can now, for example, group them according to whatever parts of their file names you wish:

GatherBy[imported , #[[1, 2]] &][[1]]

(* 
 ==>

{{{"Electric", "A", "1"}, "Test{1}"}, {{"Electric", "A", "2"}, "Test{2}"}, 
   {{"Electric", "A", "3"}, "Test{3}"}}


*)