Below is a quick sketch of vertical arrays
constructed from DataReader.
--- Raul Miller <[EMAIL PROTECTED]> wrote:
> On 2/26/07, Oleg Kobchenko <[EMAIL PROTECTED]> wrote:
> > Are there unit tests of samples for this class?
>
> I don't know how to write portable instances of
> DataTable objects. (DataTable does not have
> a public constructor.) There's probably some way
> to do this (perhaps involving loading a DataSet from
> an xml file), but I don't know all the details.
Attached is an example of CSV DataReader.
> That said, some of the simpler conversions could be
> tested by pushing data from J through JConvert and
> comparing that result with 3!:1 inside J. (But I've
> not tried that, yet.)
>
> > If the data intended for J comes from the database,
> > wouldn't be logical to use DataReader instead of
> > DataTable, which created a second cache of the whole
> > result in memory?
>
> [1] An extra temporary in-memory copy is not necessarily
> anything worth agonizing over.
>
> [2] I imagine constructing portable unit tests involving
> DataReader would be even more problematic than
> constructing unit tests involving DataTable.
Hmm... No. See example.
> [3] I think this would wind up being more complex to
> implement. (If nothing else, I think you wind up having
> to use GetSchemaTable to determine the basic
> structure of the table, so you wind up having to work
> with both an empty DataTable and the DataReader).
It doesn't look complex. I think it is simpler.
(DynamicMethod is not needed and replaced with
bulk switches).
> > However, the logic will have to
> > be regrouped to be able to fill separate columns
> > in parallel.
>
> Yes, that also.
>
> > Boxed result is interesting and J boxed arrays construction
> > in .NET too. But it might be more efficient to use native
> > homogenous .NET vectors for columns and pass them natively
> > into J unboxed with fixing and SetM.
>
> How do you make that work for strings (varchar
> columns)?
Strings are joined and then cut in J.
> Meanwhile, here's my current concerns:
...
============================================================[Program.cs]==
using System;
using System.Data.OleDb;
using System.Data;
using System.Text;
using System.IO;
using System.Collections.Generic;
public class MyClass {
public static void Main() {
string connectionString =
string.Format(
"Provider=Microsoft.Jet.OLEDB.4.0;" +
"Data Source={0};" +
"Extended Properties=\"text;HDR=Yes;FMT=Delimited\"",
Path.GetFullPath(Directory.GetCurrentDirectory() +
"\\..\\..\\test"));
using (OleDbConnection conn = new OleDbConnection(connectionString)) {
try {
conn.Open();
OleDbCommand myCommand = conn.CreateCommand();
myCommand.CommandType = CommandType.Text;
myCommand.CommandText =
string.Format("select * from test.csv where firstname <>
'{0}'", "Test");
System.Collections.IList[] cols;
int totalCount = 0;
using (OleDbDataReader dataReader = myCommand.ExecuteReader()) {
cols = new System.Collections.IList[dataReader.FieldCount];
System.Collections.IList list;
for (int i = 0; i < dataReader.FieldCount; i++) {
switch (Type.GetTypeCode(dataReader.GetFieldType(i))) {
case TypeCode.Int32: list = new List<int>(); break;
case TypeCode.Double: list = new List<double>(); break;
default: list = new List<string>(); break;
}
cols[i] = list;
}
while (dataReader.Read()) {
for (int i = 0; i < dataReader.FieldCount; i++) {
cols[i].Add(dataReader.GetValue(i));
}
totalCount++;
}
}
for (int i = 0; i < totalCount; i++) {
Console.WriteLine("{0}, {1}, {2}, {3}",
cols[0][i], cols[1][i], cols[2][i], cols[3][i]);
}
int[] AgeArray = new int[totalCount];
cols[2].CopyTo(AgeArray, 0);
Console.WriteLine("Array Type: {0}, Length: {1}",
AgeArray.GetType(), AgeArray.Length);
string[] NameArray = new string[totalCount];
cols[0].CopyTo(NameArray, 0);
Console.WriteLine("String Array: {0}", string.Join("|",
NameArray));
} catch (Exception ex) {
Console.WriteLine(ex.Message);
Console.WriteLine(ex.StackTrace);
}
}
Console.WriteLine("all done.");
}
}
===========================================================[test.csv]==
FirstName,LastName
John,Doe,25,1.2
James,Fox,35,100
Adam,Smith,45,0.345
==========================================================[schema.ini]==
[test.csv]
ColNameHeader=True
Format=CSVDelimited
MaxScanRows=25
CharacterSet=ANSI
Col1=FirstName Char Width 20
Col2=LastName Char Width 20
Col3=Age Integer
Col4=Value Double
========================================================================
Sample output:
John, Doe, 25, 1.2
James, Fox, 35, 100
Adam, Smith, 45, 0.345
Array Type: System.Int32[], Length: 3
String Array: John|James|Adam
all done.
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