This is a question about the Histogram Data Analysis tool.

By default, Excel seems to apply some (unclear) heuristic
for determining the number of bins.

Is there an easy way for me to force the number of bins
to be N?

The operative word is "easy".

I know that the tool allows me to specify a "bin range",
a range of cells that specify the lower bound of each bin.

But that seems "hard" for me use because the range of data
cells change, based on the number of data points I want to
include in the histogram.

I might (please confirm) be able to assign an array name
to a data cell range, then constuct an N-cell bin range
that uses the min() and max() of the array name. By
reassigning the array name to different data cell ranges,
the bin range values should change automatically.

But it would be "easier" if the histogram tool allowed me
to simply specify the number of bins, and the tool computed
the lower bound based on the data range, as I would.

I am looking for something that "easy". Since the need
seems so "obvious" and "common", I suspect I am simply
failing to see how to do it.

joeu2004 -

This is a question about the Histogram Data Analysis tool. By default,
Excel seems to apply some (unclear) heuristic for determining the number
of bins. <

Seems to be approximately from MIN(data) to MAX(data) with INT(SQRT(n))
bins.

Is there an easy way for me to force the number of bins to be N? The
operative word is "easy". <

I don't think so. I think you need to use your judgment.

I know that the tool allows me to specify a "bin range", a range of cells
that specify the lower bound of each bin. <

No, I think each bin value is the inclusive upper bound of a value range.

But that seems "hard" for me use because the range of data cells change,
based on the number of data points I want to include in the histogram. I
might (please confirm) be able to assign an array name to a data cell
range, then constuct an N-cell bin range that uses the min() and max() of
the array name. By reassigning the array name to different data cell
ranges, the bin range values should change automatically. But it would be
"easier" if the histogram tool allowed me to simply specify the number of
bins, and the tool computed the lower bound based on the data range, as I
would. I am looking for something that "easy". Since the need seems so
"obvious" and "common", I suspect I am simply failing to see how to do it.
<

I don't think it's "easy" at all. As I said, I think you need to use your
judgment. Most people find histograms easier to interpret if the bin values
are multiples of 2, 4, or 5. And most people prefer to have more bins when
the number of values in the data set is larger. An algorithm that
incorporates "nice" intervals is not trivial.

You might be interested in looking at the "Better Histogram" page at
www.treeplan.com to see a solution to a related histogram issue.

- Mike

www.mikemiddleton.com

Michael R Middleton wrote:
[joeu2004 wrote:]
Is there an easy way for me to force the number of bins to be N?
The operative word is "easy".

I don't think so. I think you need to use your judgment.

Sorry to hear that.

I know that the tool allows me to specify a "bin range",
a range of cells that specify the lower bound of each bin.

No, I think each bin value is the inclusive upper bound of a
value range.

You are probably right. When I reread the Histogram Help
description, I realize that it is not written in my native
language, English.

First, it says: "Microsoft Excel counts the number of data
points between the current bin number and the adjoining higher
bin, if any."

I think that supports my interpretation. It would not make
sense to count a number in one bin, if the bin boundary value
is the upper bound for the bin and the number is "between
the current [upper] bin [value] and the [upper bin value of]
the adjoining higher bin".

But in fact, then it says: "A number is counted in a particular
bin if it is equal to or less than the bin number down to the
last bin."

I think the English translation is: "A number is counted in
the highest-valued bin for which the number is less than or
equal to the bin's boundary value."

I had trouble gronking "DOWN to the LAST bin", especially since
the following sentance says: "All values below the first bin
value are counted together, as are the values above the last
bin value."

If the bin values are in "ascending order", I think "down"
would be in the direction of descending values. Yet, "last
bin" clearly refers to the highest-valued bin.

Oh well, thanks so much for clarifying.

You might be interested in looking at the "Better Histogram" page at
www.treeplan.com to see a solution to a related histogram issue.

Interesting. The Excel's banal histogram chart never bothered
me because, frankly, I did not know about it. I always chart
the data that is generated by the Histogram tool. In fact, I
choose an XY Scatter diagram.

I do wish that the X-axis values were the midpoint of the bins.
Of course, it is "easy" enough for me to add a column to compute
that.

Thanks again for confirming my suspicion that there is no easy
way to control the number of bins.