This may not address your question directly, but should provide you with directions on alternates to MorrisJS.
require(rCharts)
tmp <- data.frame(
a = c(1, 2, 3, 4, 5),
b = c(0.1, 0.2, 0.3, 0.4, 0.5),
c = c(0.2, 0.3, 0.4, 0.5, 0.6)
)
options(stringsAsFactors = F)
library(reshape2)
tmp_m = melt(tmp, id = "a")
library(rCharts)
# NVD3
nPlot(value ~ a, group = 'variable', data = tmp_m, type = 'lineChart')
# Polychart
rPlot(value ~ a, color = 'variable', data = tmp_m, type = 'line')
# Highcharts
hPlot(value ~ a, group = 'variable', data = tmp_m, type = 'line')