**Software for Exploratory Data Analysis and Statistical Modelling**, and kindly contributed to R-bloggers)

In previous posts (here and here) we created a simple function that returns a single numeric value. In some situations it may be more useful to return a more flexible data type, such as a list object, to provide more information about the calculations that have been performed.

We can extend our previous function by changing the return value to a list including the height and width supplied by the user. The last line of the function is changed to:

list(Height = height, Radius = radius, Volume = volume)

This creates a list with three elements, which are given very obvious names. The function in full is:

cylinder.volume.4 = function(height, radius) { if (missing(height)) stop("Need to specify height of cylinder for calculations.") if (missing(radius)) stop("Need to specify radius of cylinder for calculations.") if (height < 0) stop("Negative height specified.") if (radius < 0) stop("Negative radius specified.") volume = pi * radius * radius * height list(Height = height, Radius = radius, Volume = volume) }

We can call this function using a simple example:

> cylinder.volume.4(20, 4) $Height [1] 20 $Radius [1] 4 $Volume [1] 1005.310

The output from this function is a list with three slots as discussed above.

This approach is ideally suitable to statistical applications where we might have a model with a large amount of supplementary information that should be returned after it has been applied to a set of data.

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**Software for Exploratory Data Analysis and Statistical Modelling**.

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