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Re: [Pytables-users] modifying a table column
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From: Anthony S. <sc...@gm...> - 2013-08-27 23:58:39
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On Tue, Aug 27, 2013 at 6:50 PM, Oleksandr Huziy <guz...@gm...>wrote: > 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) > 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 <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 >>> >>> >>> ------------------------------------------------------------------------------ >>> 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 >>> Pyt...@li... >>> https://lists.sourceforge.net/lists/listinfo/pytables-users >>> >>> >> >> >> ------------------------------------------------------------------------------ >> 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 >> Pyt...@li... >> https://lists.sourceforge.net/lists/listinfo/pytables-users >> >> > > > ------------------------------------------------------------------------------ > 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 > Pyt...@li... > https://lists.sourceforge.net/lists/listinfo/pytables-users > > |
