fillcol.R

# Find winner and percent of votes secured
candidates = names(df)[4:9];                                
df$winner  = candidates[apply(df[, candidates], 1, which.max)];    
df$winpct  = apply(df[, candidates], 1, max);

# Assign palettes to winners
df$colpal = sapply(df$winner, switch, 
  'braun'    = 'PuRd', 'chico'    = 'Greens',
  'delvalle' = 'Oranges', 'emanuel'  = 'Purples');

# Bin winner's pct votes secured
df$bins = cut(df$winpct, c(0, 50, 75, 100), 
               labels = F, include.lowest = T);

# Choose fill colors
df = adply(df, 1, transform, 
       fillcol = brewer.pal(5, colpal)[bins + 2]);

# Plot choropleth
choro3 = plotChoropleth(.poly = chicago, .df   = df,
  id1 = list('WARD', 'PRECINCT'),
  id2 = list('ward', 'precinct'),
  fill  = 'fillcol', 
  title = 'Chicago Mayoral Elections 2011',
  legtitle = 'Pct Votes for Winner',
  colpal = 'Blues', n = 5, style = 'pretty') +
  opts(legend.position = c(0.15, 0.25))