Entering Data into a Data File
==============================

First you need to enter some data into a file. Open your editor and
start entering the data
shown below:

.. _my_exp_1: 

.. figure:: pictures/data_file.png
   :align: center
   :alt: The text version of this example data is my_exp_1.data in the example directory.	
   :scale: 60 %
   
   Fig.1: Structure of a data file


Now save the file as ``my_exp_1.data`` (this is the standard format of
a :class:`LT.datafile.dfile` object). I prefer to give the data
files the extension ``.data`` in order to distinguish them from other
files.

This example shows the four main parts of a data
file.

#. *Comment lines* (starting with a  ``#`` in the first column) are
   ignored by the program and are used to add information that you might
   later find useful for yourself.

#. *Parameter definition lines*. These **ALWAYS** start with ``#\``. In
   this way you can enter values which are common to all data points.

#. **THE HEADER LINE**, this is the most important line and **MUST BE
   PRESENT**. It always starts with ``#!`` followed by the names of
   the variables of the data entered below in column form.

#. Each columns is represented by ``name[dtype, col.nr.]/``,  *dtype* is the data type and *col.nr*
   (starting at 0) is the column number, **do not forget the / at the end of the name**

#. Data types:

      - s : string
      - f : float
      - i : integer

6. blank lines are ignored   

#. *Data lines*. Each line of  **MUST** have the same number of
   data as you have variable names in the header line. In the end each variable name
   labels a column of data.


Preparing data files should be done before you start the experiments
and is part of your preparation for your next lab session. Entering data into a file is what one of you can do during the
experiment and/or what you need to do when you start analyzing the
data. These data can now be used in python using the (LabTool) :mod:`LT.box` for
further analysis.