Todos Logos posted an article on Statistic on aiR - Sep 17, 2011, 4:44 pm
I implemented in R a function to re-create the CDC Growth Chart, according to the data provided by the CDC. In order to use this function, you need to download the .rar file available at this megaupload link Then unrar the file, and put the Growth folder in your main directory, as selected in R. You...
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Todos Logos posted an article on Statistic on aiR - Sep 7, 2011, 10:43 am
Capabilities of R are definitely unless! After my previous posts about some easy image editing in R (they are here, and here), now is the time to explore if R is capable of sound editing! Just for fun, here I created a function that receives a phone number (or another sequence of numbers), and retur...
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Todos Logos posted an article on Statistic on aiR - Aug 29, 2011, 5:11 am
Here I implemented in R some dithering algorithms: - Floyd-Steinberg dithering - Bill Atkinson dithering - Jarvis-Judice-Ninke dithering - Sierra 2-4a dithering - Stucki dithering - Burkes dithering - Sierra2 dithering - Sierra3 dithering For each algorit...
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Todos Logos posted an article on Statistic on aiR - Aug 25, 2011, 5:30 pm
Benford's law, also called the first-digit law, states that in lists of numbers from many (but not all) real-life sources of data, the leading digit is distributed in a specific, non-uniform way. According to this law, the first digit is 1 about 30% of the time, and larger digits occur as the leadin...
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Todos Logos posted an article on Statistic on aiR - Jun 16, 2011, 3:52 am
x y # plot scatterplot and the regression line mod1 plot(x, y, xlim=c(min(x)-5, max(x)+5), ylim=c(min(y)-10, max(y)+10)) abline(mod1, lwd=2) # calculate residuals and predicted values res pre # plot distances between points and the regression line segments(x, y, x, pre, col="red") # add labels (r...
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Todos Logos posted an article on Statistic on aiR - Nov 7, 2010, 5:40 am
Here I present some functions I wrote to recreate some of the most common image effect available in all image editor. They require the library rimage. To load the image, use: y read.jpeg("path") To display the image, use: plot(y) Original image Sepia tone rgb2sepia function(img){ iRed img[,,1]...
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Todos Logos posted an article on Statistic on aiR - Oct 19, 2010, 2:13 pm
Very similar to what has been done to create a function to perform fast multiplication of large matrices using the Strassen algorithm (see previous post), now we write the functions to quickly calculate the inverse of a matrix. To avoid rewriting pages and pages of comments and formulas, as I did fo...
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Todos Logos posted an article on Statistic on aiR - Oct 18, 2010, 9:31 am
I tried to implement the Strassen's algorithm for big matrices multiplication in R. Here I present a pdf with some theory element, some example and a possible solution in R. I'm not a programmer, so the function is not optimize, but it works. I want to thank G. Grothendieck: suggested me a very nice...
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Todos Logos posted an article on Statistic on aiR - Oct 6, 2010, 6:47 am
For some theory on the standard IEEE-754, you can read the Wikipedia page. Here I will post only the code of the function to make the conversion in R. First we write some functions to convert decimal numbers to binary numbers: decInt_to_8bit q r xx for(i in 1:precs){ xx[1] q[i] r[i] xx[i+1] } rr r...
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Todos Logos posted an article on Statistic on aiR - Apr 28, 2010, 12:22 pm
This is the code to perform the Bhapkar V test. I've rapidly wrote it, in 2 hours. The code is then quite brutal and it could be done better. As soon as possible, I will correct it. WARNING: it works *ONLY* with 3 groups, for now! bhapkar.test.3g sample for(i in 1:length(data1)){ sample } obs for(...
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Todos Logos posted an article on Statistic on aiR - Jan 6, 2010, 7:21 am
The Latin square design is used where the researcher desires to control the variation in an experiment that is related to rows and columns in the field. Remember that: * Treatments are assigned at random within rows and columns, with each treatment once per row and once per column. * There a...
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Todos Logos posted an article on Statistic on aiR - Jan 6, 2010, 7:21 am
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Todos Logos posted an article on Statistic on aiR - Sep 5, 2009, 2:26 pm
Suppose we want to create a polynomial that can approximate better the following dataset on the population of a certain Italian city over 10 years. The table summarizes the data: $$\begin{tabular}{|1|1|}\hline Year & Population\\ \hline 1959&4835\\ 1960&4970\\ 1961&5085\\ 1962&5160\\ 1963&5310\\ 196...
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Todos Logos posted an article on Statistic on aiR - Sep 5, 2009, 2:26 pm
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Todos Logos posted an article on Statistic on aiR - Aug 25, 2009, 2:44 pm
This post is a summary of my two previous posts on the trend analysis with the Cox-Stuart test and on simple linear regression. The goal that we propose is to assess the trend in the number of visits received from a site over a long time. I use Google Analytics, because this tool allows us to save t...
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Todos Logos posted an article on Statistic on aiR - Aug 25, 2009, 2:44 pm
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Todos Logos posted an article on Statistic on aiR - Aug 20, 2009, 6:43 am
In this post we will see briefly how to implement a logistic regression model if you have categorical variables, or qualitative, organized in double entry contingency tables. In this model the dependent variable (Y) and independent variable (X) are both dichotomies (or Bernoullian). In general, the ...
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Todos Logos posted an article on Statistic on aiR - Aug 20, 2009, 6:43 am
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Todos Logos posted an article on Statistic on aiR - Aug 8, 2009, 3:59 am
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Todos Logos posted an article on Statistic on aiR - Aug 8, 2009, 3:59 am
The Cox-Stuart test is defined as a little powerful test (power equal to 0.78), but very robust for the trend analysis. It is therefore applicable to a wide variety of situations, to get an idea of the evolution of values obtained. The proposed method is based on the binomial distribution. In R ther...
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Todos Logos posted an article on Statistic on aiR - Aug 7, 2009, 2:28 pm
The one-way analysis of variance is a useful technique to verify if the means of more groups are equals. But this analysis may not be very useful for more complex problems. For example, it may be necessary to take into account two factors of variability to determine if the averages between the group...
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Todos Logos posted an article on Statistic on aiR - Aug 7, 2009, 2:28 pm
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Todos Logos posted an article on Statistic on aiR - Aug 6, 2009, 1:30 am
We use the regression analysis when, from the data sample, we want to derive a statistical model that predicts the values of a variable (Y, dependent) from the values of another variable (X, independent). The linear regression, which is the simplest and most frequent relationship between two quantit...
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Todos Logos posted an article on Statistic on aiR - Aug 6, 2009, 1:30 am
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Todos Logos posted an article on Statistic on aiR - Aug 5, 2009, 1:30 am
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Todos Logos posted an article on Statistic on aiR - Aug 5, 2009, 1:30 am
If you have qualitative variable, it is possible to verify the correlation by studying a contingency table R by C, using the Pearson's Chi-squared test. A casino wants to study the correlation between the modes of play and the number of winners by age group, to see if the number of winners depends o...
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Todos Logos posted an article on Statistic on aiR - Aug 4, 2009, 1:30 am
We saw in the previous post, how to study the correlation between variables that follow a Gaussian distribution with the Pearson product-moment correlation coefficient. If it is not possible to assume that the values follow gaussian distributions, we have two non-parametric methods: the Spearman's ...
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Todos Logos posted an article on Statistic on aiR - Aug 4, 2009, 1:30 am
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Todos Logos posted an article on Statistic on aiR - Aug 3, 2009, 3:33 am
Suppose you want to study whether there is a correlation between 2 sets of data. To do this we compute the Pearson product-moment correlation coefficient, which is a measure of the correlation (linear dependence) between two variables X and Y; then we compute the value of a t-test to study the signi...
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Todos Logos posted an article on Statistic on aiR - Aug 3, 2009, 3:33 am
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Todos Logos posted an article on Statistic on aiR - Jul 31, 2009, 4:46 am
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Todos Logos posted an article on Statistic on aiR - Jul 30, 2009, 3:32 am
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