Plotting smoothed tide charts with -twoway-

[Michael McCulloch]

Hello, I am seeking to create a twoway graph of date/time vs. tide height, in which the data points are connected by a smooth "roller-coaster" line. Is this possible?
The data structure is:

    day    ht                 date  
    Thu   2.2   01jan2015 01:43:00  
    Thu   6.5   01jan2015 08:15:00  
    Thu   -.3   01jan2015 15:08:00  
    Thu   4.7   01jan2015 22:03:00  
    Fri   2.4   02jan2015 02:38:00  
    Fri   6.5   02jan2015 08:59:00  
    Fri   -.6   02jan2015 15:52:00  
    Fri   4.9   02jan2015 22:54:00  
    Sat   2.5   03jan2015 03:28:00  
    Sat   6.5   03jan2015 09:41:00  
    Sat   -.7   03jan2015 16:32:00

Commands I've used are:

twoway connected ht date

, which creates a jagged line, and

twoway lowess ht date

or

twoway lpoly ht date

both create a statistical conversion that no longer displays the diurnal tide variations day by day. I believe what I need is a command that would interpolate between the x/y data coordinates, but not sure how to tackle that.

[William Lisowski]

Using your 11 observations of sample data, I got a plot that might look like what I imagine you're looking for with

twoway mspline ht date, bands(11)

In this example, I told Stata to nail each data point exactly (hence the same number of bands as observations) and connect them with a cubic spline.



I am assuming that your interest lies in producing an illustrative plot. If you are intrerested in statistical analysis of your data, you should perhaps be looking into capabilities described in Stata's [TS] Time-Series Reference Manual.