ReadList and ToExpression

Question

My dataset is like:

id, feat_1, feat_2, feat_8, feat_9, feat_10, feat_11, feat_17, feat_18, feat_22, feat_2, target

1, 1, 0, 0, 0, 0, 1, 2, 0, 1, 0, Class_1
2, 0, 0, 1, 0, 0, 0, 0, 2, 0, 0, Class_1

The file is very large, so I don't want to use 'Import". Therefore I would like to use 'ReadList'

strm = OpenRead["test.TXT"];
Skip[strm, String, 1];
dataM = ToExpression@
  ReadList[strm, Table[Record, {12}], NullRecords -> True, 
   RecordSeparators -> {",", "\n"}]
Close[strm];

The output is: {1, 1, 0, 0, 0, 0, 1, 2, 0, 1, 0, Class_}

The integer in 'Class_1" disapeared. If I don't use 'ToExpression@' then all integers are seen as strings ("1", "1"....)

Anyone a suggestion how to solve this issue

Answer 1

The underscore _ as a pattern matching mechanism is reserved for mathematica. Therefore, either use something like

dataM = ReadList[strm, Table[Record, {12}], NullRecords -> True, 
RecordSeparators -> {",", "\n"}];

output = Table[Flatten[{ToExpression[Drop[dataM[[i]], -1]], Last[dataM[[i]]]}],
{i,1,Length[dataM]}];

or remove the underscore in your data file.