1

I have a Raster Stack with 32 Raster Layers. What I want to do is to calculate the median for each Raster and also the 0.25 and 0.75 quantiles. Then I want to convert the results into a dataframe.

For the median I have allready found a quite simple solution:

#calculate median and convert to dataframe

median.df <- data.frame(cellStats(r_stack, "median"))

The Problem is, that I can´t do the same with the quantiles, since cellStats cant calculate that.

My best approach with the quantiles so far was:

quant <- calc(r_stack, fun = function(x) 
          {quantile(x,probs = c(.25,.75),na.rm=TRUE)} )

quant.df <- as.data.frame(quant)

But the dataframe has 16644 rows instead of the expected 32.

2

You can supply a function to cellStats - here on a 5 layer example:

> cellStats(r_stack, function(s,...){quantile(s,probs=c(.25,.75))})
      layer.1   layer.2   layer.3   layer.4   layer.5
25% 0.3613589 0.2072302 0.3314491 0.3160375 0.1740109
75% 0.8063743 0.8571872 0.8297163 0.6712669 0.7010024

that's a matrix but save that as m and a quick flip to a dataframe is easy enough:

> data.frame(t(m))
             X25.      X75.
layer.1 0.3613589 0.8063743
layer.2 0.2072302 0.8571872
layer.3 0.3314491 0.8297163
layer.4 0.3160375 0.6712669
layer.5 0.1740109 0.7010024

quick check, this should match the third row:

> quantile(r_stack[[3]],probs=c(.25,.75))
      25%       75% 
0.3314491 0.8297163 
  • Thank you very much Spacedman! The code works for me after I added na.rm=TRUE in the quantile function. – Felix Tischer Sep 17 '18 at 12:50

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