修复 plotly 色标中断

Question

我使用 plotly 的 R 界面创建了一个热图，如下所示：

df <- data.frame(date = rep(seq(ymd('2016-09-01'), ymd('2016-09-10'), by='day'), each=2),
                 period = rep(c('lunch', 'dinner'), times=10),
                 diff=rnorm(20))

df %>%
  plot_ly(x = date,
          y = period,
          z = abs(diff),
          type = "heatmap",
          hoverinfo='none',
          colors = rev(RColorBrewer::brewer.pal(5, "RdYlGn")),
          showscale = F) %>%
  add_trace(x = date,
            y = period,
            text = paste0(round(diff*100), '%'),
            mode='text',
            hoverinfo='none')

产生这个：

有什么办法可以修复色标断裂的问题吗？我希望色标的中点为 20%，任何超过 50% 的值都在色标末端用红色着色。

Answer 1

好吧，热图通常应该具有随元素值而变化的颜色，但您可以根据您想要的任何标准将每个元素强制分为 5 组中的 1 组，并相应地分配 5 种颜色。然后，该分组将传递到 z。 z 应该是一个数字，而不是一个因子，因此您可以将分组转换为整数：

# create 5 levels or groups for the diff variable
# choose breaks as desired
diffLevel <- cut(abs(df$diff),
                 breaks = c(0, 0.0625, .125, .3, .5, Inf))

df %>%
  plot_ly(x = date,
          y = period,
          z = as.integer(diffLevel),
          type = "heatmap",
          hoverinfo='none',
          colors = rev(RColorBrewer::brewer.pal(5, "RdYlGn")),
          showscale = F) %>%
  add_trace(x = date,
            y = period,
            text = paste0(round(diff*100), '%'),
            mode='text',
            hoverinfo='none')

另一种方法是将 zmax 值设置为 0.5（和 zauto = FALSE）。这不一定会将色标的中心设置为 .2，但它工作得很好，并建立了 0.5 的截止值，高于该值的一切都是红色的。它还允许你直接传入abs(diff)：

df %>%
  plot_ly(x = date,
          y = period,
          z = abs(diff),
          zauto = FALSE,  # set this to FALSE!
          zmax = 0.5,              
          type = "heatmap",
          hoverinfo='none',
          colors = rev(RColorBrewer::brewer.pal(5, "RdYlGn")),
          showscale = F) %>%
  add_trace(x = date,
            y = period,
            text = paste0(round(diff*100), '%'),
            mode='text',
            hoverinfo='none')

最后一种方法是使用自定义色阶。我发现这很难以正确的格式获取 colorscale 参数。可能有更好的方法来做到这一点，但我无法想出任何优雅的方法。

customPalette <- colorRampPalette(c("red", "yellow", "green"))(61) 
# I put 30 values between 0 and .2 and and 30 between .2 and 1.
# And so, my palette has 61 colors  
customColors <- setNames(
  data.frame(breaks =  c(seq(0, .2, length.out = 31), seq(.21, 1, length.out = 30)),
             colors = as.character(
              apply(col2rgb(rev(customPalette)), 2, function(ii)
                paste("rgb(", paste(ii, collapse = ","),")", sep = ""))),
             stringsAsFactors = FALSE),
  NULL)
# not perfect, but it seems to work decently

# initialize a list
colList <- list() 
colList[[dim(customColors)[1]]] <- 0

# format custom color list
for(i in seq_len(dim(customColors)[1])) {
  colList[[i]] <- c(customColors[i, 1], customColors[i, 2])
}

# set zmax = 0.5 and zauto = FALSE
df %>%
  plot_ly(x = date,
          y = period,
          z = abs(diff),
          zauto = FALSE,
          zmax = 0.5,
          type = "heatmap",
          hoverinfo='none',
          colorscale =  colList,
          showscale = F) %>%
  add_trace(x = date,
            y = period,
            text = paste0(round(diff*100), '%'),
            mode='text',
            hoverinfo='none')

修复 plotly 色标中断

fix plotly color scale breaks

r

plotly