Re: Reposted, Reformatted Re: "mapping" functions over lists, again!
- To: mathgroup at smc.vnet.net
- Subject: [mg96337] Re: Reposted, Reformatted Re: "mapping" functions over lists, again!
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Thu, 12 Feb 2009 06:32:50 -0500 (EST)
- Organization: The Open University, Milton Keynes, UK
- References: <gmu8ik$geb$1@smc.vnet.net>
In article <gmu8ik$geb$1 at smc.vnet.net>,
"Paul Ellsmore" <paul.ellsmore at nanion.co.uk> wrote:
> This is a repost of an earlier post, as there were problems with the email
> formatting for some people. I have composed this one in Notepad, and cut and
> pasted to Outlook. Hope it works better.
You should try to copy and past Mathematica expressions in InputForm[],
for it is way more readable and far less prone to misinterpretation
(especially when your email/newsgroup client adds spurious equal sings
and/or other unwanted characters or character conversions).
To use the _InputForm_ when copying an expression from a Mathematica
notebook to an email client: select the cell(s) you want to include in
your email, then within the *Cell* menu select either *Convert To* or
*Display As* and choose *InputForm*. Finally, copy and paste as usual.
> Thanks to all who have already given me some advice, but I still haven't
> quite got it yet!
>
> My data is in the form:
>
> shortTestdata = {{{40., 28.06776 + 1.208548*I}, {43.094, 28.05721 +
> 1.298519*I}, {46.428, 28.05527 + 1.400228*I}, {50.019, 28.05509 +
> 1.508759*I},
> {53.888, 28.05729 + 1.624517*I}, {58.057, 28.05651 + 1.75026*I}}, {{40.,
> 7.42169 + 0.2198589*I}, {43.094, 7.408397 + 0.2343525*I},
> {46.428, 7.403769 + 0.2521353*I}, {50.019, 7.401313 + 0.2715986*I},
> {53.888, 7.400478 + 0.2920617*I}, {58.057, 7.39994 + 0.3145005*I}},
> {{40., 1685.526 + 0.04809976*I}, {43.094, 1694.691 - 0.09133625*I},
> {46.428, 1698.265 - 0.02731824*I}, {50.019, 1699.761 - 0.0491538*I},
> {53.888, 1700.523 - 0.2179222*I}, {58.057, 1701.162 - 0.2423136*I}},
> {{40., 1808.702 - 0.006286621*I}, {43.094, 1808.524 - 0.1140757*I},
> {46.428, 1808.534 - 0.02445889*I}, {50.019, 1808.443 - 0.1061664*I},
> {53.888, 1808.481 - 0.1762974*I}, {58.057, 1808.631 - 0.2894506*I}}}
>
> This is a list of lists, the lowest level lists containing pairs of {real,
> complex}. The individual lists are not all the same length, and the total
> number of lists can vary, and I need to preserve the list structure.
[snip]
I suggest to use the replacement operator "/." (w/o the quotation marks)
to apply the transformation rule. In doing so, the structure of the
original list will be preserved. Therfore, rather than Cases[] or Map[],
you could use
shortTestdata /. {r_Real, c_Complex} :> {r, Re[c]}
For instance, here is a complete example applied to your data:
In[1]:= shortTestdata = {{{40., 28.06776 + 1.208548*I}, {43.094,
28.05721 + 1.298519*I}, {46.428, 28.05527 + 1.400228*I}, {50.019,
28.05509 + 1.508759*I}, {53.888,
28.05729 + 1.624517*I}, {58.057, 28.05651 + 1.75026*I}}, {{40.,
7.42169 + 0.2198589*I}, {43.094,
7.408397 + 0.2343525*I}, {46.428,
7.403769 + 0.2521353*I}, {50.019,
7.401313 + 0.2715986*I}, {53.888,
7.400478 + 0.2920617*I}, {58.057, 7.39994 + 0.3145005*I}}, {{40.,
1685.526 + 0.04809976*I}, {43.094,
1694.691 - 0.09133625*I}, {46.428,
1698.265 - 0.02731824*I}, {50.019,
1699.761 - 0.0491538*I}, {53.888,
1700.523 - 0.2179222*I}, {58.057,
1701.162 - 0.2423136*I}}, {{40.,
1808.702 - 0.006286621*I}, {43.094,
1808.524 - 0.1140757*I}, {46.428,
1808.534 - 0.02445889*I}, {50.019,
1808.443 - 0.1061664*I}, {53.888,
1808.481 - 0.1762974*I}, {58.057, 1808.631 - 0.2894506*I}}};
In[2]:= Dimensions[shortTestdata]
Out[2]= {4, 6, 2}
In[3]:= lst = shortTestdata /. {r_Real, c_Complex} :> {r, Re[c]}
Out[3]= {{{40., 28.0678}, {43.094, 28.0572}, {46.428,
28.0553}, {50.019, 28.0551}, {53.888, 28.0573}, {58.057,
28.0565}}, {{40., 7.42169}, {43.094, 7.4084}, {46.428,
7.40377}, {50.019, 7.40131}, {53.888, 7.40048}, {58.057,
7.39994}}, {{40., 1685.53}, {43.094, 1694.69}, {46.428,
1698.27}, {50.019, 1699.76}, {53.888, 1700.52}, {58.057,
1701.16}}, {{40., 1808.7}, {43.094, 1808.52}, {46.428,
1808.53}, {50.019, 1808.44}, {53.888, 1808.48}, {58.057,
1808.63}}}
In[4]:= Dimensions[lst]
Out[4]= {4, 6, 2}
HTH,
--Jean-Marc