Change List<Object> into List<List<int>> using LINQ - arrays

Question

I have an application using the following model:
namespace myapp.Models.Types
{
public class PressureRowT
{
public System.DateTime Timestamp { get; set; }
public int P1{ get; set; }
public int P2{ get; set; }
public int P3{ get; set; }
public int P4{ get; set; }
public int P5{ get; set; }
}
}
I have a List< PressureRowT > with approximately 5000 elements, generated by parsing files. I need to plot the pressure by passing the data to chart.js for data viewing. For that, I would need a JSON array like:
[Timestamp: [date1, date2, date3... daten], P1: [val1, val2, val3, ..., valn], P2: [val1, val2, val3, ..., valn] ... P5: [val1, val2, val3, ..., valn]]
What would be the most efficient way of "inverting" the structure ?
Thank you in advance.

Answer 1

Assuming right now you have a list of PressureRowT and you want an object PressureRowT with lists within it, you can use something like
var Timestamps = pressureRowTList.Select(pressureRowT => pressureRowT.TimeStamp).ToList();
for each of the fields and assign them all to one object.

Answer 2

The most efficient way would be to re-write your parsing code to build the correct structures as the files are read.
Barring that, the best thing to do is not use LINQ, but simply build the Lists needed. A for loop is more efficient than a foreach when processing a List:
var src = new List<PressureRowT>();
var srccount = src.Count;
var PR_TS = new List<DateTime>(srccount);
var PR_P1 = new List<int>(srccount);
var PR_P2 = new List<int>(srccount);
var PR_P3 = new List<int>(srccount);
var PR_P4 = new List<int>(srccount);
var PR_P5 = new List<int>(srccount);
for (int j1 = 0; j1 < srccount; ++j1) {
PR_TS.Add(src[j1].Timestamp);
PR_P1.Add(src[j1].P1);
PR_P2.Add(src[j1].P2);
PR_P3.Add(src[j1].P3);
PR_P4.Add(src[j1].P4);
PR_P5.Add(src[j1].P5);
}
var ans = new { Timestamp = PR_TS, P1 = PR_P1, P2 = PR_P2, P3 = PR_P3, P4 = PR_P4, P5 = PR_P5 };

Answer 3

I might use Aggregate to build up the result object:
IEnumerable<PressureRowT> values;
var resultSeed = new {
Timestamp = new List<DateTime>(),
P1 = new List<int>(),
P2 = new List<int>(),
P3 = new List<int>(),
P4 = new List<int>(),
P5 = new List<int>(),
};
return values.Aggregate(
resultSeed,
(result, value) => {
result.Timestamp.Add(value.Timestamp);
result.P1.Add(value.P1);
result.P2.Add(value.P2);
result.P3.Add(value.P3);
result.P4.Add(value.P4);
result.P5.Add(value.P5);
return result;
});