Plots are not stored in list during loop

Question

I have a problem similar to what is found here. I have a loop which runs through some modelling for different pairs of variables. Probably should not have used loops to go through them, but right now that is too late. Then I want to create a plot for each run. At first nothing showed before looking at that post. Looking at the post and implementing the best answer i could at least print the plots, but they still were not stored. The idea is to generate the plots, and then use grid.arrange to plot them together. Could someone show how to fix it? Here is some random data and the loop from example:

col1 <- c(2, 4, 1, 2, 5, 1, 2, 0, 1, 4, 4, 3, 5, 2, 4, 3, 3, 6, 5, 3, 6, 4, 3, 4, 4, 3, 4, 
      2, 4, 3, 3, 5, 3, 5, 5, 0, 0, 3, 3, 6, 5, 4, 4, 1, 3, 3, 2, 0, 5, 3, 6, 6, 2, 3)
col2 <- c(2, 4, 4, 0, 4, 4, 4, 4, 1, 4, 4, 3, 5, 0, 4, 5, 3, 6, 5, 3, 6, 4, 4, 2, 4, 4, 4, 
      1, 1, 2, 2, 3, 3, 5, 0, 3, 4, 2, 4, 5, 5, 4, 4, 2, 3, 5, 2, 6, 5, 2, 4, 6, 3, 3)
col3 <- c(2, 5, 4, 1, 4, 2, 3, 0, 1, 3, 4, 2, 5, 1, 4, 3, 4, 6, 3, 4, 6, 4, 1, 3, 5, 4, 3, 
      2, 1, 3, 2, 2, 2, 4, 0, 1, 4, 4, 3, 5, 3, 2, 5, 2, 3, 3, 4, 2, 4, 2, 4, 5, 1, 3)

data2 <- data.frame(col1,col2,col3)
data2[,1:3] <- lapply(data2[,1:3], as.factor)
colnames(data2)<- c("A","B","C")

myplots <- vector('list', ncol(data2))

for (i in seq_along(data2)) {
    message(i)
    myplots[[i]] <- local({
        i <- i
    p1 <- ggplot(data2, aes(x = data2[[i]])) +
        geom_histogram(fill = "lightgreen") +
        xlab(colnames(data2)[i])
    print(p1)
 })
}

I tried to change print to return, but to no avail. I get the plots printed in the View window in Rstudio, but the plots are not stored at all.

score 2 · Accepted Answer · answered Apr 05 '21 at 08:17

You can use the following code -

library(ggplot2)

myplots <- vector('list', ncol(data2))

for (i in seq_along(data2)) {
  myplots[[i]] <- ggplot(data2, aes(x = .data[[colnames(data2)[i]]])) +
      geom_histogram(fill = "lightgreen")
}

However, using lapply would be easier.

myplots <- lapply(names(data2), function(x)  
        ggplot(data2, aes(x = .data[[x]])) + geom_histogram(fill = "lightgreen"))

Plot the list of plots with grid.arrange.

gridExtra::grid.arrange(grobs = myplots)

data

A <- c(2, 4, 1, 2, 5, 1, 2, 0, 1, 4, 4, 3, 5, 2, 4, 3, 3, 6, 5, 3, 6, 4, 3, 4, 4, 3, 4, 
          2, 4, 3, 3, 5, 3, 5, 5, 0, 0, 3, 3, 6, 5, 4, 4, 1, 3, 3, 2, 0, 5, 3, 6, 6, 2, 3)
B <- c(2, 4, 4, 0, 4, 4, 4, 4, 1, 4, 4, 3, 5, 0, 4, 5, 3, 6, 5, 3, 6, 4, 4, 2, 4, 4, 4, 
          1, 1, 2, 2, 3, 3, 5, 0, 3, 4, 2, 4, 5, 5, 4, 4, 2, 3, 5, 2, 6, 5, 2, 4, 6, 3, 3)
C <- c(2, 5, 4, 1, 4, 2, 3, 0, 1, 3, 4, 2, 5, 1, 4, 3, 4, 6, 3, 4, 6, 4, 1, 3, 5, 4, 3, 
          2, 1, 3, 2, 2, 2, 4, 0, 1, 4, 4, 3, 5, 3, 2, 5, 2, 3, 3, 4, 2, 4, 2, 4, 5, 1, 3)
data2 <- data.frame(A,B,C)

PKumar · Answer 2 · 2021-04-05T09:59:07.023

Does this work for you?, With patchwork and purrr::reduce we can club these graphs to stack(horizontal or vertical) with each other. You can also use slashes(/) instead of plus(+) in reduce to make it appended vertically instead of horizontally. If you want to plot histogram you should have continuous data , In case you do want to plot counts for discrete data you should try geom_bar. If you do want to check for geom_bar then you need to convert the columns into factors. I am not so sure what plot you want to carry out, I am assuming that you have continuous data and you want to carry out histogram here. Please let me know if it doesn't work in your scenario.

library(tidyverse)
library(patchwork)
data2 <- data.frame(col1, col2, col3) ## No conversion of factors

nm <- names(data2)
g1 <- reduce(map2(data2,nm, ~ggplot(data2,aes(x =.x )) + geom_histogram(fill = "yellow4") + labs(x=.y, y = 'count')), `+`)

print(g1)

Or with slashes:

g2 <- reduce(map2(data2,nm, ~ggplot(data2,aes(x =.x )) + geom_histogram(fill = "yellow4") + labs(x=.y, y = 'count')), `/`)

print(g2)

Or if you want to have for loops then probably you can do this as well, you already have intialised myplots so not adding it here:

for (i in seq_along(data2)) {
  myplots[[i]] <- 
    ggplot(data2, aes(x = data2[[i]])) +
      geom_histogram(fill = "lightgreen") +
      xlab(colnames(data2)[i])
}

Explanation:

Now you can use reduce with your myplots to arrange them, Note here myplots should be containing your 3 plots :

reduce(myplots, `+`)

for arranging it.

The map2 and reduce is similar solution, with map2 you are getting 3 plots saved into a list, so 3 objects are returned from below code:

plots <- map2(data2,nm, ~ggplot(data2,aes(x =.x )) + geom_histogram(fill = "yellow4") + labs(x=.y, y = 'count'))

To add them (arrange) them all you have to do is to use patchwork like below: plots[[1]] + plots[[2]] + plots[[3]], but then its quite cumbersome, so we use reduce to make it happen like below:

reduce(plots, `+`)

Also like I mentioned earlier you can use slash instead of plus to make the arrangement vertical than horizontal. with plot_layout option in patchwork, you can create more flexible plots. You can check here .

with gridExtra : gridExtra::grid.arrange(grobs = (myplots)), again instead of myplots, it can be any list that contain ggplot objects.

Plots are not stored in list during loop

2 Answers2