Re: [Pytables-users] modifying a table column

2013-08-27 Thread Anthony Scopatz 
Glad I could help!


On Tue, Aug 27, 2013 at 7:44 PM, Oleksandr Huziy wrote:

> 2013/8/27 Anthony Scopatz 
>
>>
>> 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 * m", uservars = {"c": c, "m": coef })
>> expr.set_output(c)
>> expr.eval()
>> varTable.flush()
>> h.close()
>>
>
> Aha, this is cool. Thanks Anthony.
>
> Cheers
> --
> Sasha
>
>
>>
  On Tue, Aug 27, 2013 at 11:44 AM, Oleksandr Huziy <
 [email protected]> 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
>
>
> --
> Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more!
> Discover the easy way to master current and previous Microsoft
> technologies
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>


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Re: [Pytables-users] modifying a table column

2013-08-27 Thread Oleksandr Huziy 
2013/8/27 Anthony Scopatz 

>
> 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 * m", uservars = {"c": c, "m": coef })
> expr.set_output(c)
> expr.eval()
> varTable.flush()
> h.close()
>

Aha, this is cool. Thanks Anthony.

Cheers
--
Sasha


>
>>>  On Tue, Aug 27, 2013 at 11:44 AM, Oleksandr Huziy <
>>> [email protected]> 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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Re: [Pytables-users] modifying a table column

2013-08-27 Thread Anthony Scopatz 
On Tue, Aug 27, 2013 at 6:50 PM, Oleksandr Huziy wrote:

> Hi Again:
>
>
> 2013/8/27 Anthony Scopatz 
>
>> 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 > > 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
>>>
>>>
>>> --
>>> Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more!
>>> Discover the easy way to master current and previous Microsoft
>>> technologies
>>> and advance your career. Get an incredible 1,500+ hours of step-by-step
>>> tutorial videos with LearnDevNow. Subscribe today and save!
>>>
>>> http://pubads.g.doubleclick.net/gampad/clk?id=58040911&iu=/4140/ostg.clktrk
>>> ___
>>> Pytables-users mailing list
>>> [email protected]
>>> https://lists.sourceforge.net/lists/listinfo/pytables-users
>>>
>>>
>>
>>
>> --
>> Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more!
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>> technologies
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>>
>>
>
>
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Re: [Pytables-users] modifying a table column

2013-08-27 Thread Oleksandr Huziy 
Hi Again:


2013/8/27 Anthony Scopatz 

> 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 
> 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
>>
>>
>> --
>> Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more!
>> Discover the easy way to master current and previous Microsoft
>> technologies
>> and advance your career. Get an incredible 1,500+ hours of step-by-step
>> tutorial videos with LearnDevNow. Subscribe today and save!
>>
>> http://pubads.g.doubleclick.net/gampad/clk?id=58040911&iu=/4140/ostg.clktrk
>> ___
>> Pytables-users mailing list
>> [email protected]
>> https://lists.sourceforge.net/lists/listinfo/pytables-users
>>
>>
>
>
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Re: [Pytables-users] modifying a table column

2013-08-27 Thread Oleksandr Huziy 
Thank you Anthony.

Cheers


2013/8/27 Anthony Scopatz 

> 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
>
>
> On Tue, Aug 27, 2013 at 11:44 AM, Oleksandr Huziy 
> 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
>>
>>
>> --
>> Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more!
>> Discover the easy way to master current and previous Microsoft
>> technologies
>> and advance your career. Get an incredible 1,500+ hours of step-by-step
>> tutorial videos with LearnDevNow. Subscribe today and save!
>>
>> http://pubads.g.doubleclick.net/gampad/clk?id=58040911&iu=/4140/ostg.clktrk
>> ___
>> Pytables-users mailing list
>> [email protected]
>> https://lists.sourceforge.net/lists/listinfo/pytables-users
>>
>>
>
>
> --
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Re: [Pytables-users] modifying a table column

2013-08-27 Thread Anthony Scopatz 
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


On Tue, Aug 27, 2013 at 11:44 AM, Oleksandr Huziy 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
>
>
> --
> Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more!
> Discover the easy way to master current and previous Microsoft technologies
> and advance your career. Get an incredible 1,500+ hours of step-by-step
> tutorial videos with LearnDevNow. Subscribe today and save!
> http://pubads.g.doubleclick.net/gampad/clk?id=58040911&iu=/4140/ostg.clktrk
> ___
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> https://lists.sourceforge.net/lists/listinfo/pytables-users
>
>
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