output formatting - How to apply multiple format to a list

I have a nested list like

matrix = {{1.2345664, 2.38673956, 3.567846}, {0.00034554, 124.4554654,
6.34543}, {0.0000233, 244.34454, 2}}

and I want to apply MatrixForm, but also NumberForm[,{5,4}], because I want that in every element of the matrix the numbers are properly padded.

Is this possible in some way?

Interestingly perhaps, I want eventually write the resulting output list in a file.

P.S.: Now I write with Export["my_file.dat",Flatten[matrix]], and after I obtain the proper padding using a C program. But there must be a clever way...

Answer

You can do this a couple of different ways. This is easiest:

NumberForm[MatrixForm @ matrix, {5, 4}]

This works because NumberForm affects sub-expressions including ones wrapped in MatrixForm. You can do it the other way but it's more complicated:

Map[NumberForm[#, {5, 4}] &, matrix, {2}] // MatrixForm

---

You mention that you eventually want to export this. You should not need (or use) MatrixForm for export. The question of export of NumberForm formatted numbers may be answered here: How can I control the number format of exported data? In version 7 however the Accepted answer does not work. You might use something like:

Export[
 "myfile.dat"
 Map[ToString @ NumberForm[#, {5, 4}] &, matrix, {2}],
 "Table"
]