On Tue, Aug 27, 2013 at 6:50 PM, Oleksandr Huziy <guziy.sa...@gmail.com>wrote:
> Hi Again:
>
>
> 2013/8/27 Anthony Scopatz <scop...@gmail.com>
>
>> Hey Sasha,
>>
>> You probably want to look at the Expr class [1] where you set "out" to be
>> the same as the original array.
>>
>> Be Well
>> Anthony
>>
>> 1. http://pytables.github.io/usersguide/libref/expr_class.html
>>
>
>
> I just wanted to make sure if it is possible to use an assignment in
> expressions? (this gives me a syntax error exception, complains about the
> equal sign in the expression)
>
Hi Sasha,
Assignment is a statement not an expression, so it is not possible to use
here. This is why you are getting a syntax error.
>
> h = tb.open_file(path, mode="a")
> varTable = h.get_node("/", var_name)
> coef = 3 * 60 * 60 #output step
> expr = tb.Expr("c = c * m", uservars = {"c": varTable.cols.field, "m":
> coef })
> expr.eval()
> varTable.flush()
> h.close()
>
> Is this an optimal way of multiplying a column? (this one works, but I
> think it loads all the data into memory...right?)
>
> expr = tb.Expr("c * m", uservars = {"c": varTable.cols.field, "m":
> coef })
> varTable.cols.field[:] = expr.eval()
>
You are right that this loads the entire computed array into memory and is
therefore not optimal. I would do something like the following:
h = tb.open_file(path, mode="a")
varTable = h.get_node("/", var_name)
coef = 3 * 60 * 60 #output step
c = varTable.cols.field
expr = tb.Expr("c = c * m", uservars = {"c": c, "m": coef })
expr.set_output(c)
expr.eval()
varTable.flush()
h.close()
Be Well
Anthony
>
> Thank you
>
> Cheers
>
>
>>
>>
>> On Tue, Aug 27, 2013 at 11:44 AM, Oleksandr Huziy <guziy.sa...@gmail.com
>> > wrote:
>>
>>> Hi All:
>>>
>>> I have a huge table imported from other binary files to hdf, and I
>>> forgot to multiply the data by a factor in one case. Is there an easy way
>>> to multiply a column by a constant factor using pytables?
>>> To modify it in place?
>>>
>>> Thank you
>>>
>>> --
>>> Sasha
>>>
>>>
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>>
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>
>
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