Record array help


[I've also asked this on scipy-user, but since 'csv2rec' is a pylab function which is not part of NumPy, I thought maybe someone here can give me some pointers...]

Is there any extended documentation/tutorial on record arrays? The NumPy
book is pretty cryptic about this and I'm still very new to the concept. I'm
using the csv2rec function from matplotlib (pylab) to generate a record
array from data that's in a CSV file. The CSV file basically has column
labels in the first row and numerical data in all subsequent rows. The
issues I'm struggling with are:

1. Is it possible to change the dtype of a field after the record array has
been created?

2. The CSV file has missing data points - how do I turn these into python
'None' elements in the record array? (If I leave that element empty in the
CSV file, then csv2rec complains about not being able to handle the import;
if I put 'None' in the CSV file (without quotes), then the whole field
including the 'None' and all the other float data is converted into a string
dtype, rendering the numerical data useless).

3. Is it possible to obtain a subset of the original data (corresponding to
two or more columns of the CSV file) as a conventional 2D numpy array, or
can I access the data only individually by column (i.e. field in the record

Any pointers would be appreciated!