[R] Loop with ggplot2 not as simple as it seems...

[PIKAL Petr]

Hi Patricia

You are somewhat circling around solution.

Is this what you wanted?

for (i in 5:7) {
  plotname = paste("Graph", names(scores)[i], sep="")
  png(paste0(plotname,".png"))
  p <- ggplot(scores, aes(x=scores[,i], fill=gender ))
  print(p+ geom_density(alpha=.3)+xlab(names(scores)[i]))
dev.off()
}

Cheers
Petr


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Patricia Seo
> Sent: Tuesday, October 28, 2014 1:59 AM
> To: r-help at r-project.org
> Subject: [R] Loop with ggplot2 not as simple as it seems...
>
> Hi everyone,
>
> I have been battling with this problem for the past month and reading
> all that I can about it, but I just can't seem to understand what I'm
> doing wrong. It seems easy and I can replicate others well-recorded
> attempts, but can not seem to apply this to my data.
>
> I have created a data.frame to easily illustrate my problem. I would
> like to plot columns 5:7 in my data without having to write-out-every-
> single-variable name. In this example it is only three columns but in
> my actual data set it is more like 50 columns. Here is the simplified
> data frame:
>
> sid <- c(1001:1010) #student id
> age <- c(10, 12, 14, 15, 13, 16, 14, 12, 14, 10)
> race <- race <- c("w", "b", "a", "w", "a", "w", "b", "a", "w", "a")
> gender <- gender <-c("M", "F", "M", "F", "M", "F", "M", "F", "M", "F")
> read <- rnorm(10, 100, 50)
> write <- rnorm(10, 100, 50)
> math<-rnorm(10, 100, 50)
>
> scores <- data.frame(sid, age, race, gender, read, write, math)
>
> My end goal is to produce a .png like this for every column:
>
> ggplot(scores, aes(x=scores$read, fill=scores$gender)) +
> geom_density(alpha=.3)
>
> In other words, I would like to write a loop that would produce
> separate .pngs for each column. No facet-wrap. I would like one plot
> showing the distribution of one score for male and female in one .png
> file.
>
> Failed Attempt #1 of 3: My first attempt was to melt data since I know
> ggplot2 likes melted data. I have tried melting the data using sid,
> age, race and gender as the id variable. But I’m not sure how to plot
> what I would like above with just using values. In my actual data set
> there are over 50 columns to plot (instead of the simple three in the
> example scores data). I tried creating:
>
> xobject <- subset(scores.melt, variable=read)
>
> but it gives me the error: Don't know how to automatically pick scale
> for object of type data.frame. Defaulting to continuous
> Error: Aesthetics must either be length one, or the same length as the
> dataProblems:test1
>
> Failed Attempt #2 of 3: My second attempt is below but it had similar
> problems to what others have mentioned with ggplot changing the names
> of each plot but keeping the last known data column so all the graphs
> look the same. It works in terms of titles but not data! And I have
> tried as_string() but to no avail:
>
> for (i in 5:7) {
>   column_to_plot = as.character(paste("Col_", i, sep=""))
>   png(paste0("Graph", column_to_plot,".png"))
>   ggplot(scores, aes(x=column_to_plot, fill=gender )) +
> geom_density(alpha=.3)
>   ggsave(paste0("Graph", column_to_plot,".png"))
>
> }
>
> Failed Attempt #3 of 3: My third attempt is my most successful attempt.
> It is because I created a vector that includes the list of variables I
> would like to plot. Unfortunately, I have two problems with this
> method: (1) Don’t know how to include the corresponding title name so I
> know which plot corresponds to the score even though I do indicate the
> names of the Indexes, and (2) It is annoying to have to write the
> entire list of variables I want to plot especially if there are 50
> variable names. I know I can specify columns 5:7 (like above) but I’m
> not grasping the logics of this loop:
>
> Indexes = list()
> Indexes[[1]] = scores$read
> Indexes[[2]] = scores$write
> Indexes[[3]] = scores$math
>
> names(Indexes) = c(“Scores for Read“,
>                    “Scores for Write”, “Scores for Math“)
>
> ##### for some reason, I have to run the top half and after it has
> processed that, run the bottom half#####
>
> for(i in seq(along = Indexes)) {
>   Index = Indexes[[i]]
>
>   for(j in 1:length(gender)) {
>     png(paste0("Graph", Index,".png"))
>     ggplot(scores, aes(x=Index, fill = gender)) +
> geom_density(alpha=.3)
>     ggsave(paste0("Graph", Index,".png"))
>
>   }
> }
>
> Any help would be much appreciated. I know this is a frankenstein from
> previous questions and problems with loops in ggplot2, but just
> understand what I'm doing wrong would even be a huge help.
>
> ______________________________________________
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> guide.html
> and provide commented, minimal, self-contained, reproducible code.

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