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  • In R, how do you get the best fitting equation to a set of data?

    - by Matherion
    I'm not sure wether R can do this (I assume it can, but maybe that's just because I tend to assume that R can do anything :-)). What I need is to find the best fitting equation to describe a dataset. For example, if you have these points: df = data.frame(x = c(1, 5, 10, 25, 50, 100), y = c(100, 75, 50, 40, 30, 25)) How do you get the best fitting equation? I know that you can get the best fitting curve with: plot(loess(df$y ~ df$x)) But as I understood you can't extract the equation, see Loess Fit and Resulting Equation. When I try to build it myself (note, I'm not a mathematician, so this is probably not the ideal approach :-)), I end up with smth like: y.predicted = 12.71 + ( 95 / (( (1 + df$x) ^ .5 ) / 1.3)) Which kind of seems to approximate it - but I can't help to think that smth more elegant probably exists :-) I have the feeling that fitting a linear or polynomial model also wouldn't work, because the formula seems different from what those models generally use (i.e. this one seems to need divisions, powers, etc). For example, the approach in Fitting polynomial model to data in R gives pretty bad approximations. I remember from a long time ago that there exist languages (Matlab may be one of them?) that do this kind of stuff. Can R do this as well, or am I just at the wrong place? (Background info: basically, what we need to do is find an equation for determining numbers in the second column based on the numbers in the first column; but we decide the numbers ourselves. We have an idea of how we want the curve to look like, but we can adjust these numbers to an equation if we get a better fit. It's about the pricing for a product (a cheaper alternative to current expensive software for qualitative data analysis); the more 'project credits' you buy, the cheaper it should become. Rather than forcing people to buy a given number (i.e. 5 or 10 or 25), it would be nicer to have a formula so people can buy exactly what they need - but of course this requires a formula. We have an idea for some prices we think are ok, but now we need to translate this into an equation.

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  • What is the best way to set default values in ActiveRecord?

    - by ryw
    What is the best way to set default value in ActiveRecord? I see a post from Pratik that describes an ugly, complicated chunk of code: http://m.onkey.org/2007/7/24/how-to-set-default-values-in-your-model class Item < ActiveRecord::Base def initialize_with_defaults(attrs = nil, &block) initialize_without_defaults(attrs) do setter = lambda { |key, value| self.send("#{key.to_s}=", value) unless !attrs.nil? && attrs.keys.map(&:to_s).include?(key.to_s) } setter.call('scheduler_type', 'hotseat') yield self if block_given? end end alias_method_chain :initialize, :defaults end YUCK! I have seen the following examples googling around: def initialize super self.status = ACTIVE unless self.status end and def after_initialize return unless new_record? self.status = ACTIVE end I've also seen people put it in their migration, but I'd rather see it defined in the model code. What's the best way to set default value for fields in ActiveRecord model?

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  • What is the best way to store categorical references in SQL tables?

    - by jlafay
    I'm wanting to store a wide array of categorical data in MySQL database tables. Let's say that for instance I want to to information on "widgets" and want to categorize attributes in certain ways, i.e. shape category. For instance, the widgets could be classified as: round, square, triangular, spherical, etc. Should these categories be stored within a table to reference them best from an application? Another possibility, I would imagine, would be to add a column to widgets that contained a shape column that contained a tiny int. That way my application could search shapes by that and then use a coordinating enum type that would map the shape int meanings. Which would be best? Or is there another solution that I'm not thinking of yet?

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  • Best Practice for Exporting an App's Data to XML via PHP/MySQL?

    - by Alex Cook
    I have an a business app and I want to give my users the ability to export their data at anytime. I'm aware that I can write an XML file semi-manually by doing something like this: http://www.kirupa.com/web/mysql_xml_php.htm But, I thought I'd ask if this is the best practice? Or is there some framework I can use to do this more easily/quickly? Maybe there isn't - it won't be too hard to do it the above way. Also, less importantly - XML is the best format to export to, right? Thanks in advance.

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  • Best approach to update a control after an Ajax request?

    - by Cuga
    I have a webpage that fires off an Ajax request which stores some data to a database and I want to update the webpage so that the user can see their changes have been submitted. There are at least 3 ways I can think of accomplishing this: Immediately update the webpage with plain JavaScript by grabbing the contents of the user's inputted text and immediately inserting it where it belongs. Have the ajax call return the stored text as the response, grab the response, and then insert this text where it belongs on the page using JavaScript Have the ajax call return a flag (say, true for successful db write, false otherwise), and if the flag is true, use JavaScript to grab the user's contents from the input control and insert it where it belongs elsewhere on the page Or another method not mentioned...? I don't mean this to be subjective, I just don't know which would be the best method to apply. My instinct tells me to go with the third item (return a flag, then update the field). Is this the best way? Thanks

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  • What is the best way to do multiple listviews in android?

    - by Nicos
    Hi all, i am writing a software that i have to drill down on content a lot. For example when the program starts a listview is displayed. When user clicks on an item, then a second listview must be displayed. For example: Select Continent Select Country Select State Select City Select Address What is the best way to do this (less memory, faster, easier to code etc)? To create multiple listviews with multiple adapters? Or 1 listview with multiple Adapters? Lists are loaded from an external XML File. So far i am creating a new adapter and setting it to the listview. How do i create a second listview and after clicking on 1st listview displaying the second one, with animation. Any examples? Extend my class to ListActivity or Activity? Best regards and thanks for helping, Nicos

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  • Which is the best and appropriate way to write the code in Winforms ?

    - by Harikrishna
    What is the best way to write the code ? (1) Like directly writing the code in the button_click() event. or (2) Make the function of that code which I write in button_click() event and write this function in one class and then that function I should call in the button_Click() event.Like is it called three-tired approach to write the code ? Like in button_Click() event I write the code to save the records in csv file from datatable.So I should write that code in button_Click() event or I should make one new function and one new class and write that code in that function which is the new class and calling that function in button_Click() event. This is only one example but I am talking about all the code written in my application that which is the appropriate and best way to write the code and what are the benefits ? Note that I write the code in Winforms with c#.

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