Re: [Pytables-users] modifying a table column

[Oleksandr H. <guz...@gm...>]

Hi Again:


2013/8/27 Anthony Scopatz <sc...@gm...>

> 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)

    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()

Thank you

Cheers


>
>
>  On Tue, Aug 27, 2013 at 11:44 AM, Oleksandr Huziy <guz...@gm...>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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