如何在圖像圖中爲NA分配特定顏色

Question

我正在使用image命令繪製矩陣，該矩陣包含一些NA值。我使用image像

image(figData, zlim = zRange, col = colors, useRaster=TRUE) 

zRange比figData的實際範圍小。我使用下面的一組，這與紅綠色彩感知不足兼容的頂部顏色表：

http://www.mathworks.com/matlabcentral/fx_files/31761/6/thumbnail_184481.jpg

我想在figData來選擇NA值的特定顏色是外面colors（例如，gray）。 NA值現在映射到最後一個元素colors（white），因此我無法將它們與超出範圍的值區分開來。

理想情況下，我想要一個解決方案，無論我使用哪種調色板。

我想要類似於選項heatmap.2，我該怎麼辦？我願意修改image源代碼來完成此操作，但image似乎稱爲rasterImage函數，其源代碼無法找到。

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接受Jealie的回答後，我在這裏包括代碼考慮到不同的下面和上面的範圍值：

image.nan <- function(z, zlim, col, na.color='gray', outside.below.color='black', outside.above.color='white',...) 
{ 
    zstep <- (zlim[2] - zlim[1])/length(col); # step in the color palette 
    newz.below.outside <- zlim[1] - zstep # new z for values below zlim 
    newz.above.outside <- zlim[2] + zstep # new z for values above zlim 
    newz.na <- zlim[2] + 2 * zstep # new z for NA 

    z[which(z<zlim[1])] <- newz.below.outside # we affect newz.below.outside 
    z[which(z>zlim[2])] <- newz.above.outside # we affect newz.above.outside 
    z[which(is.na(z>zlim[2]))] <- newz.na # same for newz.na 

    zlim[1] <- zlim[1] - zstep # extend lower limit to include below value 
    zlim[2] <- zlim[2] + 2 * zstep # extend top limit to include the two new values above and na 

    col <- c(outside.below.color, col, outside.above.color, na.color) # we construct the new color range by including: na.color and na.outside 

    image(z=z, zlim=zlim, col=col, ...) # we finally call image(...) 
} 

Answer 1

小的修正：值之外沒有被映射到col最後一個元素，但他們卻沒有被繪製（並且沒有顏色看起來是白色的）。

否則，要回答您的問題，最簡單的方法是在image附近編寫一個包裝，其中包含兩個新參數：na.color和outside.color。這是我的建議，該建議默認爲gray爲NA值和white爲值以外zlim：

my.image <- function(figData, zlim, col, na.color='gray', outside.color='white', ...) 
{ 
    newz.na <- zlim[2]+(zlim[2]-zlim[1])/length(col) # new z for NA 
    newz.outside <- zlim[2]+2*(zlim[2]-zlim[1])/length(col) # new z for values outside zlim 

    figData$z[which(is.na(figData$z>zlim[2]))] <- newz.na # we affect newz.outside 
    figData$z[which(figData$z<zlim[1] | figData$z>zlim[2])] <- newz.outside # same for newz.na 


    zlim[2] <- zlim[2]+2*(zlim[2]-zlim[1])/length(col) # we finally extend the z limits to include the two new values 

    col <- c(col, na.color, outside.color) # we construct the new color range by including: na.color and outside.color 

    image(figData, zlim=zlim, col=col, ...) # we finally call image(...) 
} 

Answer 2

由於彩色間隔等(*bottom*, *top*]定義，沿z是相等的值，以zlim [1]將與被着色outside.below.color（因爲outside.below.color的範圍是(*zlim[1] - zstep* , *zlim[1]* ]）。

以下版本修正了這個錯誤：

image.nan.better <- function(z, zlim, col, na.color='gray', outside.below.color='black', outside.above.color='white',...) 
{ 
     zstep <- (zlim[2] - zlim[1])/length(col); # step in the color palette 
     newz.below.outside <- zlim[1] - 2 * zstep # new z for values below zlim 
     newz.above.outside <- zlim[2] + zstep # new z for values above zlim 
     newz.na <- zlim[2] + 2 * zstep # new z for NA 

     z[which(z<zlim[1])] <- newz.below.outside # we affect newz.below.outside 
     z[which(z>zlim[2])] <- newz.above.outside # we affect newz.above.outside 
     z[which(is.na(z>zlim[2]))] <- newz.na # same for newz.na 

     zlim[1] <- zlim[1] - 2 * zstep # extend lower limit to include below value 
     zlim[2] <- zlim[2] + 2 * zstep # extend top limit to include the two new values above and na 

     col <- c(outside.below.color, col[1], col, outside.above.color, na.color) #correct by including col[1] at bottom of range 

     image(z=z, zlim=zlim, col=col, ...) # we finally call image(...) 
} 

比較：

f = matrix(abs(rnorm(300)),nrow=50) 
f[which(f>1)]=1 

f[44,4] = 0 
f[41,4] = NA 
f[42,4] = NA 
f[43,4] = NA 
f[44,3] = -1 
f[44,5] = 2 

image(as.matrix(f),col=c('green3','green2','blue1','blue3'),zlim=c(0,1)) 

image.nan(as.matrix(f),col=c('green3','green2','blue1','blue3'),zlim=c(0,1),outside.below.color='red',outside.above.color='brown',na.color='yellow') 

image.nan.better(as.matrix(f),col=c('green3','green2','blue1','blue3'),zlim=c(0,1),outside.below.color='red',outside.above.color='brown',na.color='yellow')