R help - May 2011 - How is the relation between Frequency and Counts in hist/density defined?

Hi all,
I'm looking to add a "density" smoother on top of a hist when
Freq=T.
In order to do this I can use the relation between count and density, but I
would like to know if there is a way for me to predict it upfront.

Here is an example:

set.seed(242)
z = rnorm(30)
hist_z <- hist(z)
hist_z$counts / hist_z$density # the relation is 15
# why is this 15 ??
# So I can now do:
hist(z)
y <- density(z)$y  * max(hist_z$counts / hist_z$density, na.rm = T) # this
is what I hope to find without using hist, and only using density
x <- density(z)$x
lines(x = x, y = y, col = "blue", lwd = 5)


Thanks in advance,
Tal


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> In order to do this I can use the relation between count and density, but
   I
   > would like to know if there is a way for me to predict it upfront.
   In the code for hist.default, you'll see the line
   dens <- counts/(n * diff(breaks))
   > Here is an example:
   >
   > set.seed(242)
   > z = rnorm(30)
   > hist_z <- hist(z)
   > hist_z$counts / hist_z$density # the relation is 15
   In your example, n is 30, and the breaks are evenly spaced every 0.5.
   Regards,
   Richie.
   Mathematical Sciences Unit
   [1]HSL
   [2]4D Pie Charts
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References

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