Candlesticks chart is a plot used
primarily in finance for describing price movements of quoted stock,
derivative or currency over time. It is a combination of a line-chart
and a bar-chart:
 |
| Chart made by R package "Quantmod" |
the wick (i.e. one or two lines coming
out from the polygon) illustrates the highest and lowest traded
prices during the time interval represented; the body (i.e. the
polygon) illustrates the opening and closing trades. Candlesticks
chart
seems apparently similar
to box plots, but they are totally different (source:
Wikipedia,
05/02/2013).
I often saw this kind of chart in
newspapers or in TV, but only now I have undertaken to understand how
it works; and so I had the “crazy” idea of applying candlesticks
chart to archaeological data.
More specifically I thought about
archaeological finds. For many of them - in particular for ceramic
types - we know a starting date, i.e. the period in which a
specific production begins, a time range of maximum
diffusion,
defined by an initial moment and a final one, and an end
date after which there are no more traces of our object.
If we replace the 4 financial values of
higest, lowest, opening and closing price with these 4 chronological
value (starting date, initial and final moments of maximum diffusion's range, end date), we could use profitably candle plot for describing the life's
path of each archaeological material found in a stratigraphic unit
(US); the goal is to date the same US by comparing the candlesticks
of all materials contained therein.
In R Candlesticks chart is provided by Quantmod package, Quantitative Financial Modelling & Trading
Framework for R
(
http://cran.r-project.org/web/packages/quantmod/index.html).
But this package is very specific for financial purposes and requires
specific data types like time series (xts): so I put aside the idea of using the Quantmod package and I tried to build a
new R function for plotting candlesticks with non-financial data.
I built a table like this:
find, min, int_1, int_2, max
find_a, 250, 300, 400, 550
find_b, 200, 350, 400, 450
find_c, 350, 400, 450, 500
find_d, 250, 350, 450, 500
find_e, 200, 400, 500, 600
For each archaeological object (find_a,
find_b, find_c, …) is given the starting date (min), the initial
and final moments of maximum presence range (int_1, int_2) and the
end date (max), all in approximate years.
I plotted this dataframe in R using
“with()” function that enables to build a personal environment
from data. Here is the source code:
> US1
<- read.table("../example.txt", header=TRUE, sep=",")
>
with(US1, symbols(find, (int_1 + int_2)/2,
boxplots=cbind(.4,int_2-int_1,int_1-min,max-int_2,0), inches=F,
ylim=range(US1[,-1]), xaxt="n", ylab="Years (AD)",
xlab="Findings", main="Findings chronological
distribution of US 1", fg="brown", bg="orange",
col="brown"))
axis(1,seq_along(US1$find),labels=US1$find)
and here is the result:
Analyzing this plot it is possible to
deduce that the layer US1 probably dates back to the first half of
5th century A.D.; the materials find_a and find_b could be
residuals of previous ages.
As I said, this is just a simple
example, but potentialities are clear. This method enables to plot
the duration of archaeological materials and to compare the datings
of objects found in stratigraphic units for assigning them a
chronological information. The statistical environment could provide
other advantages like probabilistic analyses, confidence intervals,
etc., giving a mathematical-statistical support to the usual (and
often subjective) dating of the archaeological layers.
The next steps will be the building of
a specific R function for “archaeological” candle plot, starting
from the simple code written above, and tests to plot the duration of
archeological finds with other statistical techniques like seriation,
boxplot, etc.
Any suggestions, websites, literature
and bibliographic references about this topic, advice on R packages different from Quantmod that provide candlesticks chart without financial data are welcomed.
by Denis Francisci
