使用ggplot2的geom_image自定义点图时遭遇UnableToOpenBlob错误求助

问题背景 #

我想用自定义图片替代ggplot散点图中的普通点，数据表中有一列值为NY_Male、NY_Female、OK_Male或OK_Female，每个值对应一张特定图片。尝试了多种导入方式后仍报错，代码及错误信息如下：

原代码 #

#import library
library(ggplot2)
library(beeswarm)
library(dunn.test)
library(ggimage)
library(png)
library(RCurl)
library(grid)

#set working directory
setwd("/Users/Documents//R")

#import data
data<-read.csv("parasite3_master.csv")

# Image
URL1 = "https://firebasestorage.googleapis.com/v0/b/tick-67255.appspot.com/o/Amblyomma_americanum_tick_blue_male.png?alt=media&token=fe30dc09-5a07-4fbd-b64e-7d90a8275eef"
NY__Male = readPNG(getURLContent(URL1))

## Image 2
URL2 = "https://firebasestorage.googleapis.com/v0/b/tick-67255.appspot.com/o/Amblyomma_americanum_tick_blue.png?alt=media&token=1e44e074-107b-4933-a6f5-9b1e81a17e9e"
NY__Female = readPNG(getURLContent(URL2))

# Image 3
URL3 = "https://firebasestorage.googleapis.com/v0/b/tick-67255.appspot.com/o/Amblyomma_americanum_tick.png?alt=media&token=d8863d57-12d8-4eb1-b86b-00dd21b33f07"
OK__Female = readPNG(getURLContent(URL3))

# Image 4
URL4 = "https://firebasestorage.googleapis.com/v0/b/tick-67255.appspot.com/o/Amblyomma_americanum_tick_green_male.png?alt=media&token=75519f09-30a6-4daa-b058-bf2430cc46d7"
OK__Male = readPNG(getURLContent(URL4))

# Crop the mal image
#NY_Male = NY_Male [40:250,,]

## Turn images into raster grobs
NY_Male = rasterGrob(NY__Male)
NY_Female = rasterGrob(NY__Female)
OK_Male = rasterGrob(OK__Male)
OK_Female = rasterGrob(OK__Female)

attach(NY_Male)
attach(NY_Female)
attach(OK_Male)
attach(OK_Female)

#check work
View(data)
summary(data)

#create data object
attach(data)

#Paste Function to combine location and sex
Categories <- paste(Location, Sex, sep=" ")

#Water Balance charts
#plot QH
WBplot <- ggplot(data , 
                 aes(y = DT, x = Categories , fill = Sex)) + 
  stat_summary(fun=mean,geom="errorbar",aes(ymax=..y..,ymin=..y..)) +
  geom_dotplot(binaxis='y', stackdir='center', position=position_dodge(1), dotsize = .5)+
  geom_image(aes(image=Image, size=0.015))
  ylab("Dehydration Tolerance (%)") +
  ylim(5,40) +
  theme(axis.text = element_text(size = 12),
        axis.title = element_text(size = 15, face = "bold"),
        axis.title.x = element_blank(),
        strip.text.x = element_text(size = 15),
        strip.text.y = element_text(size = 15),
        legend.position = "top",
        panel.background = element_rect(fill = "white", colour = NA),
        panel.border = element_rect(fill = NA, colour = "black"),
        strip.background = element_rect(colour = "black"))
WBplot

报错信息 #

Error in `geom_image()`:
! Problem while converting geom to grob.
ℹ Error occurred in the 3rd layer.
Caused by error:
! rsession-arm64: UnableToOpenBlob `NY_Male': No such file or directory @ error/blob.c/OpenBlob/2924

问题原因与解决方法 #

核心错误 #

1. geom_image()参数逻辑错误：该函数的image参数需要图片的URL、本地路径，或与数据绑定的图片对象引用，你手动创建的rasterGrob对象无法通过attach()映射到数据列。
2. 未建立数据与图片的映射：代码中aes(image=Image)的Image列并未在数据表中定义，无法将分类值对应到图片。

修正步骤 #

1. 给数据表添加图片映射列

使用case_when根据Categories的值，给每条数据匹配对应的图片URL（如果用本地图片，替换为本地路径即可）：

# 加载dplyr（未安装则先运行install.packages("dplyr")）
library(dplyr)

# 生成Categories列并添加图片URL映射
data <- data %>%
  mutate(Categories = paste(Location, Sex, sep = " "),
         Image_URL = case_when(
           Categories == "NY Male" ~ "https://firebasestorage.googleapis.com/v0/b/tick-67255.appspot.com/o/Amblyomma_americanum_tick_blue_male.png?alt=media&token=fe30dc09-5a07-4fbd-b64e-7d90a8275eef",
           Categories == "NY Female" ~ "https://firebasestorage.googleapis.com/v0/b/tick-67255.appspot.com/o/Amblyomma_americanum_tick_blue.png?alt=media&token=1e44e074-107b-4933-a6f5-9b1e81a17e9e",
           Categories == "OK Female" ~ "https://firebasestorage.googleapis.com/v0/b/tick-67255.appspot.com/o/Amblyomma_americanum_tick.png?alt=media&token=d8863d57-12d8-4eb1-b86b-00dd21b33f07",
           Categories == "OK Male" ~ "https://firebasestorage.googleapis.com/v0/b/tick-67255.appspot.com/o/Amblyomma_americanum_tick_green_male.png?alt=media&token=75519f09-30a6-4daa-b058-bf2430cc46d7"
         ))

2. 移除无效的attach()操作

删掉所有attach(NY_Male)、attach(data)这类代码，attach()会污染全局环境，且无法实现图片与数据的正确映射。

3. 修正ggplot代码

直接用数据中的Image_URL列映射图片，同时调整图层位置避免重叠：

WBplot <- ggplot(data, aes(y = DT, x = Categories, fill = Sex)) + 
  stat_summary(fun = mean, geom = "errorbar", aes(ymax = ..y.., ymin = ..y..)) +
  # 若不需要原有的dotplot可删除该行，否则图片会覆盖点
  # geom_dotplot(binaxis='y', stackdir='center', position=position_dodge(1), dotsize = .5)+
  geom_image(aes(image = Image_URL), size = 0.015, position = position_dodge(1)) +
  ylab("Dehydration Tolerance (%)") +
  ylim(5, 40) +
  theme(axis.text = element_text(size = 12),
        axis.title = element_text(size = 15, face = "bold"),
        axis.title.x = element_blank(),
        strip.text.x = element_text(size = 15),
        strip.text.y = element_text(size = 15),
        legend.position = "top",
        panel.background = element_rect(fill = "white", colour = NA),
        panel.border = element_rect(fill = NA, colour = "black"),
        strip.background = element_rect(colour = "black"))

WBplot

额外注意事项 #

• 确保Categories的取值与case_when中的判断完全一致（包括空格、大小写），否则会出现映射缺失。
• 调整geom_image()的size参数时，该值是相对于绘图区域的比例，0.015可能偏小，可根据实际显示效果微调。
• 如果使用本地图片，需确保图片路径正确，且工作目录设置无误（可通过getwd()确认）。

内容的提问来源于stack exchange，提问作者L Trimm5