Data frames are lists

Most R users will know that data frames are lists. You can easily verify that a data frame is a list by typing

d <- data.frame(id=1:2, name=c("Jon", "Mark"))
d
 id name
1 1 Jon
2 2 Mark
is.list(d)
[1] TRUE

However, data frames are lists with some special properties. For example, all entries in the list must have the same length (here 2), etc. You can find a nice description of the differences between lists and data frames here. To access the first column of d, we find that it contains a vector (and a factor in case of column name). Note, that [[ ]] is an operator to select a list element. As data frames are lists, they will work here as well. Continue reading ‘Populating data frame cells with more than one value’


loss2Today I was working on a two-part procrustes problem and wanted to find out why my minimization algorithm sometimes does not converge properly or renders unexpected results. The loss function to be minimized is

\displaystyle  L(\mathbf{Q},c) = \| c \mathbf{A_1Q} - \mathbf{B_1} \|^2 + \| \mathbf{A_2Q} - \mathbf{B_2} \|^2 \rightarrow min  Continue reading ‘Beautiful plots while simulating loss in two-part procrustes problem’


qq_plot_spps_r

We teach two software packages, R and SPSS, in Quantitative Methods 101 for psychology freshman at Bremen University (Germany). Sometimes confusion arises, when the software packages produce different results. This may be due to specifics in the implemention of a method or, as in most cases, to different default settings. One of these situations occurs when the QQ-plot is introduced. Continue reading ‘QQ-plots in R vs. SPSS – A look at the differences’


Today I stumbled across a figure in an explanation on multiple factor analysis which contained pictograms.

 

abdi_mfa

Figure 1 from Abdi & Valentin (2007), p. 8.

I wanted to reproduce a similar figure in R using pictograms and additionally color them e.g. by group membership . I have almost no knowledge about image processing, so I tried out several methods of how to achieve what I want. The first thing I did was read in an PNG file and look at the data structure. The package png allows to read in PNG files. Note that all of the below may not work on Windows machines, as it does not support semi-transparency (see ?readPNG).

Continue reading ‘Using colorized PNG pictograms in R base plots’


post-logoAfter some time of using shiny I got to the point where I needed to send some arbitrary data from the client to the server, process it with R and return some other data to the client. As a client/server programming newbie this was a challenge for me as I did not want to dive too deep into the world of web programming. I wanted to get the job done using shiny and preferably as little JS/PHP etc. scripting as possible. Continue reading ‘Sending data from client to server and back using shiny’


Source: flickr, user saikofish, pic lou (http://www.flickr.com/photos/lou/2231734109/)

I recently wanted to construe a dashboard widget that contains some text and other elements using the grid graphics system. The size available for the widget will vary. When the sizes for the elements of the grobs in the widget are specified as Normalised Parent Coordinates the size adjustments happen automatically. Text does not automatically adjust though. The size of the text which is calculated as fontsize times the character expansion factor (cex) remains the same when the viewport size changes. For my widget this would require to adjust the fontsize or cex settings for each case seperately. While this is not really an obstacle, I asked myself how a grob that will adjust its text size automatically when being resized can be construed. Here I jot down my results in the hope that you may find this useful. Continue reading ‘Creating a text grob that automatically adjusts to viewport size’


on flickr by user zzpza Jan 2012, http://www.flickr.com/photos/zzpza/3269784239/. THX!In this post we collect several R one- or few-liners that we consider useful. As our minds tend to forget these little fragments we jot them down here so we will find them again. Continue reading ‘Useful R snippets’




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