Sending dataframes within list to a plot function

Question

I'm trying to make multiple ggplot charts from multiple data frames. I have developed the code below but the final loop doesn't work.

df1 <- tibble(
  a = rnorm(10),
  b = rnorm(10)
)

df2 <- tibble(
  a = rnorm(20),
  b = rnorm(20)
)

chart_it <- function(x) {
  x %>% ggplot() +
    geom_line(mapping = aes(y=a,x=b)) +
    ggsave(paste0(substitute(x),".png"))
}

ll <- list(df1,df2)

for (i in seq_along(ll)) {
 chart_it(ll[[i]])
}

I know its something to do with

ll[[i]]

but I dont understand why because when I put that in the console it gives the dataframe I want. Also, is there a way do this the tidyverse way with the map functions instead of a for loop?

dmi3kno · Accepted Answer · 2017-12-16 12:12:28Z

2

I assume you want to see two files called df1.png and df2.png at the end.

You need to somehow pass on the names of the dataframes to the function. One way of doing it would be through named list, passing the name along with the content of the list element.

library(ggplot2)
library(purrr)

df1 <- tibble(
  a = rnorm(10),
  b = rnorm(10)
)

df2 <- tibble(
  a = rnorm(20),
  b = rnorm(20)
)

chart_it <- function(x, nm) {
  p <- x %>% ggplot() +
    geom_line(mapping = aes(y=a,x=b))
  ggsave(paste0(nm,".png"), p, device = "png")
}

ll <- list(df1=df1,df2=df2)

for (i in seq_along(ll)) {
  chart_it(ll[[i]], names(ll[i]))
}

In tidyverse you could just replace the loop with the following command without modifying the function.

purrr::walk2(ll, names(ll),chart_it)

or simply

purrr::iwalk(ll, chart_it)

There's also imap and lmap, but they will leave some output in the console, which is not what you would like to do, I guess.

edited Dec 16, 2017 at 12:12

answered Dec 16, 2017 at 11:50

dmi3kno

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1 Comment

jimbo Over a year ago

That's perfect. Thanks so much :)

Roman Luštrik · Accepted Answer · 2017-12-16 11:26:55Z

0

The problem is in your chart_it function. It doesn't return a ggplot. Try saving the result of the pipe into a variable and return() that (or place it as the last statement in the function).

Something along the lines of

chart_it <- function(x) {
  chart <- x %>% ggplot() +
    geom_line(mapping = aes(y=a,x=b))

    ggsave(paste0(substitute(x),".png")) # this will save the last ggplot figure

    return(chart)
}

edited Dec 16, 2017 at 11:26

answered Dec 16, 2017 at 11:08

Roman Luštrik

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2 Comments

jimbo Over a year ago

Thanks for reply. If I run chart_it(df1) it saves the plot, so doesn't that mean my function is ok?

jimbo Over a year ago

Tried the following

chart_it <- function(x) {       x %>% ggplot() +         geom_line(mapping = aes(y=a,x=b)) +         ggsave(paste0(substitute(x),".png")) -> chart       return(chart)     }

And I get "Error: device must be NULL, a string or a function."

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