# [Numpy-discussion] Documentation for dtypes with named fields

Sam Tygier Sam.Tygier@hep.manchester.ac...
Tue Mar 16 07:47:23 CDT 2010

```Hello

I can't find much documentation for using arrays where the dtype has named fields (is there a term for this sort of array). there is some in
http://docs.scipy.org/doc/numpy/reference/arrays.dtypes.html
http://docs.scipy.org/doc/numpy/reference/generated/numpy.dtype.html
but that's most creation.

for example if i have
a = zeros(5, dtype=[('a','f'), ('b','f'), ('c','i')])
and fill it with values.

if i want to fill a row, i can do
a[0] = (0.1,0.2,3)
but if i use a list it wont work
a[0] = [0.1,0.2,3]
is there an explanation of why?

now if i wanted to do some sort of conversion, eg multiply columns 'a' and 'b' by 10, is there a way to do
a *= [10,10,1]
like i would do with a if were a zeros((5,3)) array
is
a['a'] *= 10
a['b'] *= 10
the best method?

also whats the best way to take a slice of the columns? if i want just the 'a' and 'b' columns. if it were a 2d array i could do
a[0:2]
but
a['a':'b']
does not work. is there a way to do this?

thanks

Sam
```