These routines subject your data to mathematical operations. This can be useful for bringing out features in your data, or as a necessary preprocessing step for some types of analysis.

Logarithm

The Log function in the Massage menu log-transforms your data using the natural logarithm (base e):

y=ln(x+1)

This is useful, for example, to compare your sample to a log-normal distribution or for fitting to an exponential model. Also, abundance data with a few very dominant taxa may be log-transformed in order to downweight those taxa.

Subtract mean

This function subtracts the column mean from each of the selected columns. The means can not be computed row-wise.

Remove trend

This function removes any linear trend from a data set (two columns with X-Y pairs). This is done by subtraction of a linear regression line from the Y values. Removing the trend can sometimes be a useful operation prior to spectral analysis.

Next: Plotting functions