# Using Trendlines with googleVis

A trendline is a line superimposed on a chart revealing the overall direction of the data. Google Charts can automatically generate trendlines for Scatter Charts, Bar Charts, Column Charts and Line Charts.

For more details visit: https://developers.google.com/chart/interactive/docs/gallery/trendlines

## Linear trend line

    plot(
      gvisScatterChart(women, options=list(trendlines="0"))
    )

## Exponential trend line with equation shown in legend

    plot(
      gvisScatterChart(women, options=list(
        trendlines="{0: { type: 'exponential',
                         visibleInLegend: 'true',
                         color: 'green',
                         lineWidth: 10,
                         opacity: 0.5}}",
        chartArea="{left:50,top:20,width:'50%',height:'75%'}"))
    )

## Add trend line to column chart

    dat <- data.frame(val1=c(1,3,4,5,6,8),
                      val2=c(12,23,32,40,50,55))
    plot(
      gvisColumnChart(dat,
                      options=list(trendlines="{0: {}}"))
    )

## Changing labels in legend

    dat$val3 <- c(5,6,10,12,15,20)
    plot(
      gvisColumnChart(dat,
                      options=list(trendlines="{
                              0: {
                                labelInLegend: 'Trendline 1',
                                visibleInLegend: true,},
                              1:{
                                labelInLegend: 'Trendline 2',
                                visibleInLegend: true}
                              }",
                              chartArea="{left:50,top:20,
                                          width:'50%',height:'75%'}"
                      ))
    )