Blog Archives

R Blogs

December 17, 2009
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There are many blogs on Statistics, R and other related topics scattered around the internet. The R bloggers website provides a central hub where feeds from participating blogs are collated so that they can be viewed from a single website. This resources certainly appears to be a good idea so that people can more easily identify

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The Grammar of Graphics: ggplot2 package

December 14, 2009
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The grammar of graphics approach to constructing graphs has been implemented in the ggplot2 package in R. The author of the package, Hadley Wickham, has provided a website with many details of using the system to create nice looking graphics. The package removes many of the awkward parts of setting up graphical display that characterise other

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Summarising data using bar charts

December 12, 2009
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Summarising data using bar charts

A bar graph is a frequently used type of display that compares counts, frequencies, totals or other summary measures for a series of categories, e.g. sales in different market sectors or in quarters in a financial year. The bar graph can be laid out with the categories either on the vertical or horizontal axis of

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Design of Experiments – Blocking and Full Factorial Experimental Design Plans

December 6, 2009
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When considering using a full factorial experimental design there may be constraints on the number of experiments that can be run during a particular session, or there may be other practical constraints that introduce systematic differences into an experiment that can be handled during the design and analysis of the data collected during the experiment. Blocking

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Design of Experiments – Full Factorial Designs

December 1, 2009
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In designs where there are multiple factors, all with a discrete group of level settings, the full enumeration of all combinations of factor levels is referred to as a full factorial design. As the number of factors increases, potentially along with the settings for the factors, the total number of experimental units increases rapidly. In many

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Design of Experiments – Optimal Designs

November 29, 2009
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When designing an experiment it is not always possible to generate a regular, balanced design such as a full or fractional factorial design plan. There are usually restrictions of the total number of experiments that can be undertaken or constraints on the factor settings both individually or in combination with each other. In these scenarios computer

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Design of Experiments – Power Calculations

November 18, 2009
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Prior to conducting an experiment researchers will often undertake power calculations to determine the sample size required in their work to detect a meaningful scientific effect with sufficient power. In R there are functions to calculate either a minimum sample size for a specific power for a test or the power of a test for

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Graph Examples from Visualizing Data by William Cleveland

November 12, 2009
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Graph Examples from Visualizing Data by William Cleveland

The trellis graphics approach was pioneered by various statistical researchers and the ideas are used extensively in the book “Visualizing Data” by William Cleveland. There are various resources on the website for trellis graphics including S code for creating the majority of the graphs that appear in the book. Inspired by efforts on the Learning

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Using Faceting in ggplot2 to create Trellis-like Plots

November 9, 2009
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Using Faceting in ggplot2 to create Trellis-like Plots

One of the main strengths of the Trellis graphics paradigm is the use of panelling to divide data into subsets to investigate whether patterns are consistent as the conditioning variables change. In the ggplot2 package the terminology for specifying these separate panels is faceting and can be used to create similar displays. In our previous post

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Creating scatter plots using ggplot2

November 6, 2009
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Creating scatter plots using ggplot2

The ggplot2 package can be used as an alternative to lattice for producing high quality graphics in R. The package provides a framework and hopefully simple interface to producing graphs and is inspired by the grammar of graphics. The main function for producing graphs in this package is qplot, which stands for quick plot. The first

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