[Numpy-discussion] Can I add rows and columns to recarray?
Wai Yip Tung
tungwaiyip at yahoo.com
Sun Dec 5 22:56:51 EST 2010
I'm fairly new to numpy and I'm trying to figure out the right way to do
things. Continuing on my question about using recarray as a relation. I
have a recarray like this
In [339]: arr = np.array([
.....: (1, 2.2, 0.0),
.....: (3, 4.5, 0.0)
.....: ],
.....: dtype=[
.....: ('unit',int),
.....: ('price',float),
.....: ('amount',float),
.....: ]
.....: )
In [340]: data = arr.view(recarray)
One of the most common thing I want to do is to append rows to data. I
think concatenate() might be the method. But I get a problem:
In [342]: np.concatenate((data0,[1,9.0,9.0]))
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
c:\Python26\Lib\site-packages\numpy\<ipython console> in <module>()
TypeError: expected a readable buffer object
The other thing I want to do is to calculate the column value. Right now
it can do great thing like
In [343]: data.amount = data.unit * data.price
But sometimes it may require me to add a new column not already exist,
e.g.:
In [344]: data.discount_price = data.price * 0.9
How can I add a new column? I tried column_stack. But it give a similar
TypeError. I figure I need to first specify the type of the column. But I
don't know how.
Thanks,
Wai Yip
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