Histogram function in R - breaks argument not working

Question

I like to create histogram objects per row with defined breaks:

Hist <- list()
for (i in 1:10) { 
   Hist[[i]] <- hist(data[i,],breaks=25)
}

But there is an indifference between my requirement of breaks and the number of breaks which is in the output. And also the number of breaks within the histograms is different.

Is there a reason for that?

Answer 1

To get consistent breaks, specify a vector. Not an integer, as you might have expected!

Yes there is a reason ;) From the histogram help page: ?hist:

`breaks` can be one of:
  
  1. a vector giving the breakpoints between histogram cells,
  2. a function to compute the vector of breakpoints,
  3. a single number giving the number of cells for the histogram,
  4. a character string naming an algorithm to compute the number of cells (see ‘Details’),
  5. a function to compute the number of cells.

In cases 3,4,5 the number is only a suggestion; the breakpoints will be set to pretty values. If breaks is a function, the x vector is supplied to it as the only argument.

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Note the part I've highlighted in bold.