Often I like to reduce the
alpha value (level of transparency) of colours to identify patterns of over-plotting when displaying lots of data points with R. So, here is a tiny function that allows me to add an alpha value to a given vector of colours, e.g. a
RColorBrewer palette, using
col2rgb and
rgb, which has an argument for
alpha, in combination with the wonderful
apply and sapply functions.
The example below illustrates how this function can be used with colours provided in different formats, thanks to the
col2rgb function.
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