How to export a header before the data in the result file?

Question

I would like to export a phrase to my result data as a heading.

I'm exporting the data correctly with

 Export["file.dat", table]. 

But I'm doing several simulations with different parameters and I would like to write down this parameters in the file. I'm trying with

 Write["file.dat", {"Resonance simulation Data =", DateString[], "Parametros: Nz = ", Nz, " CP = ", CP, " K1 = ", K1}]; 

but this erases the precedent data if it's put after the Export or it is erased if it came before. How could I do this?

Answer 1

You could use OpenAppend[] and Write[] instead of Export[] to persist your data.

fn = "c:\\test.dat";
s = OpenWrite@fn;
Write[s, "**Header 1 **"];
Close[s];
s = OpenAppend@fn;
Write[s, Table[i, {i, 10}]];
Close[s];
s = OpenAppend@fn;
Write[s, "**Trailer 1 **"];
Close[s];
FilePrint[fn]

"*Header 1 *"
{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
"*Trailer 1 *"

Answer 2

You can open a stream, write your header, and then pass the stream to Export:

width = 7;
height = 4;
max = 6;
table = RandomInteger[{1, max}, {width}];
st = OpenWrite["file.dat"] ; Write["file.dat", {DateString[], 
  "width = ", width, " height = ", height, " max = ", max}];
Export[st, table];
FilePrint["file.dat"]

Answer 3

I would use the following steps: 1. import the file using Import 2. prepend your header using Prepend 3. Export the data using Export

data = Import["file.dat"]
(*{{1, 2}, {3, 4}, {5, 6}}*)
headers = {"param1","param2"};
data = Prepend[data,headers]
(*{{"param1", "param2"}, {1, 2}, {3, 4}, {5, 6}}*)
Export["file.dat",data];

However, as others already mentioned there are several possible ways to do that.