program define rdsamp
    version 4.0

    preserve
    clear

    quietly{
        set obs 100
        gen x=.
        gen y=.
        gen xs=.
        gen ys=.
        gen xx=.
        gen xbar=.
    }

    global n=5
        
    wdctl button "Reset"  5  5 30 12 HJN_B0
    wdctl button "Sample" 5 20 30 12 HJN_B1
    wdctl button "Help"   5 35 30 12 HJN_B5
    wdctl button "Close"  5 50 30 12 HJN_B6
    global nnew=5
    global HJN_1 "n"
    wdctl static HJN_1 5 65 10 12 
    wdctl edit nnew 20 65 10 12
        
    global HJN_B0 "rdsampdr 0"
    global HJN_B1 "rdsampdr 1"
    global HJN_B5 "whelp rdsamp"
*    global HJN_B6 "exit 1234"
    global HJN_B6 "rdsampdr 2"

    gph open
    gph pen 1

    rdsampdr 0

    noi wdlg "Random Sampling"  5 5 80 130

    gph close

    restore

end

program define rdsampdr
    version 4.0

    local arg=`1'

    local boxcol=4

    local nx=10
    local ny=10

    local xx1=.01
    local xx2=(1./`nx')-.01
    local yy1=.01
    local yy2=(1./`ny')-.01

/* If n has changed, do a reset: */

    if $nnew < 1 | $nnew > 20 {
        sstopbox stop "n must be between 1 and 20"
        exit}

    if $n != $nnew {
        global n = $nnew
        local arg=0}

    if `arg'==0 {

        gph close
        gph open

        replace xbar=10

        replace x=uniform()
        replace y=uniform()

        graph y x, xlab(.05,.15,.25,.35,.45,.55,.65,.75,.85,.95)  ylab xscale(0,1) yscale(0,2) s(i) /* bbox(5000,0,23000,24000,850,400,0) */
        gphconv

        gph pen 1

        local ii=1
        while `ii'<=100 {

            local i=int((`ii'-1)/10)+1
            local j=mod(`ii'-1,10)+1

            local x1=$AX*(`xx1'+(`i'-1)*(1./`nx'))+$BX
            local x2=$AX*(`xx2'+(`i'-1)*(1./`nx'))+$BX
            local y1=$AY*(`yy1'+(`j'-1)*(1./`ny'))+$BY
            local y2=$AY*(`yy2'+(`j'-1)*(1./`ny'))+$BY

            gph box `y1' `x1' `y2' `x2' `boxcol'
            local ij=10*(`i'-1)+`j'
            local y111=`y1'-150
            gph text `y111' `x1' 0 -1 `ij'

        local ii=`ii'+1

        }

*        gph text 1000 1000 0 -1 Blue: Population (each box has value on x axis), Red: Sample
*        gph text 2000 2000 0 -1 Yellow: Means of Successive Samples
    }

/*  Erase old sample: */

    if `arg'==1 {

        gph pen 1
        local i=1
        while `i'<= $n {

            local x1=$AX*(`xx1'+(xs[`i']-1)*(1./`nx'))+$BX
            local x2=$AX*(`xx2'+(xs[`i']-1)*(1./`nx'))+$BX
            local y1=$AY*(`yy1'+(ys[`i']-1)*(1./`ny'))+$BY
            local y2=$AY*(`yy2'+(ys[`i']-1)*(1./`ny'))+$BY

*            gph clear int(`y2') int(`x1') int(`y1') int(`x2')
            gph box `y1' `x1' `y2' `x2' `boxcol'
*            gph box `y1' `x1' `y2' `x2' 0

            local ij=10*(xs[`i']-1)+ys[`i']
            local y111=`y1'-150
            gph text `y111' `x1' 0 -1 `ij'

            local i=`i'+1

        }

    }

    if `arg'!=2 {
/*  Get new sample: */

    gph pen 3

    replace xx=_n

    replace x=uniform()

    local i=1
    while `i' <= $n {

        local i1=`i'+int((100-`i'+1)*x[`i'])
        local i2=xx[`i1']
        replace xx=xx[`i'] in `i1'
        replace xx=`i2' in `i'

        local i=`i'+1

    }

    replace xs=int((xx-1)/10)+1
    replace ys=mod(xx-1,10)+1

    }

    local i=1
    while `i'<= $n {

        local x1=$AX*(`xx1'+(xs[`i']-1)*(1./`nx'))+$BX
        local x2=$AX*(`xx2'+(xs[`i']-1)*(1./`nx'))+$BX
        local y1=$AY*(`yy1'+(ys[`i']-1)*(1./`ny'))+$BY
        local y2=$AY*(`yy2'+(ys[`i']-1)*(1./`ny'))+$BY

        gph box `y1' `x1' `y2' `x2' 4
        if `arg'==2 {
            gph pen 3
            gph box `y1' `x1' `y2' `x2' 3}

        local i=`i'+1

    }

    if `arg'==2 {exit 1234}


/*  Draw box for average of new sample: */

    gph pen 1
    replace x=(xs-.5)/10.
    summarize x in 1/$n
    local x12=_result(3)
    local j=int(10*`x12')+1
    replace xbar=xbar+1 in `j'
    local k=xbar[`j']

    local x1=$AX*(`xx1'+(`j'-1)*(1./`nx'))+$BX
    local x2=$AX*(`xx2'+(`j'-1)*(1./`nx'))+$BX
    local y1=$AY*(`yy1'+(`k'-1)*(1./`ny'))+$BY
    local y2=$AY*(`yy2'+(`k'-1)*(1./`ny'))+$BY

    gph pen 2
    gph box `y1' `x1' `y2' `x2' `boxcol'

    local y111=`y1'-150
    local x12: display %3.2f `x12'
    gph text `y111' `x1' 0 -1 `x12'

end

exit