How to plot a in Plotly from a column name extracted from another dataframe in R

Question

I have two sample dataframes given below

library(shiny)
df1 <- data.frame(words = c("bat", "vat","cat","mat"), count = c(3420, 2098, 2003, 1501), words_count = c("bat (3420)","vat (2098)", "cat (2003)", "mat (1501)"), stringsAsFactors = FALSE)

df2 <- data.frame(class = c("A","B","C","D"), bat = c(10,0,30,20), vat = c(0,0,10,30), cat = c(20,30,0,10), mat = c(20,20,0,0), stringsAsFactors = FALSE)

Using the code below I want to extract the column name from drop down menu (made from df1) and use the extracted value to plot the bar graph in plotly using extracted value as column in df2. I am doing this is Rmd.

inputPanel(
  selectInput("words", label = "Choose the word",
              choices = df1$words_count, 
              selected = df1$words_count[1], width = '100%')
  )

renderPlot({
# Extract the word from drop down
  col_word <- df1 %>% filter(words_count == input$words) %>% pull(words)

  plot_ly(df2, x = ~category, y = ~col_word, type = 'bar') %>%
    layout(yaxis = list(title = 'Count'), xaxis = list(title = ""))
})

I get no output. I have tried a couple of things like get(col_word) however, it does not work.

Answer 1

The result col_word is a character value (eg, "bat").

For plot_ly , you need a data frame column, or list or vector, not a character string.

You can get around this in ggplot using aes_string . However, in plotly you need an alternative --- you can try:

plot_ly(df2, x = ~class, y = ~get(col_word), type = 'bar') %>%
   layout(yaxis = list(title = 'Count'), xaxis = list(title = ""))

Or:

plot_ly(df2, x = ~class, y = as.formula(paste0('~', col_word)), type = 'bar') %>%
  layout(yaxis = list(title = 'Count'), xaxis = list(title = ""))

Edit : Make sure to also use renderPlotly (note the 'ly' at the end).

Here is a full working example in R Markdown with shiny :

---
title: "Test509"
author: "Ben"
date: "5/9/2020"
output: html_document
---

```{r setup, include=FALSE}
library(shiny)
library(plotly)
library(tidyverse)
```


```{r}
df1 <- data.frame(words = c("bat", "vat","cat","mat"), count = c(3420, 2098, 2003, 1501), words_count = c("bat (3420)","vat (2098)", "cat (2003)", "mat (1501)"), stringsAsFactors = FALSE)

df2 <- data.frame(class = c("A","B","C","D"), bat = c(10,0,30,20), vat = c(0,0,10,30), cat = c(20,30,0,10), mat = c(20,20,0,0), stringsAsFactors = FALSE)

inputPanel(
  selectInput("words", label = "Choose the word",
              choices = df1$words_count, 
              selected = df1$words_count[1], width = '100%')
)

renderPlotly({
  # Extract the word from drop down
  col_word <- df1 %>% 
    filter(words_count == input$words) %>% 
    pull(words)

  plot_ly(df2, x = ~class, y = ~get(col_word), type = 'bar') %>%
    layout(yaxis = list(title = 'Count'), xaxis = list(title = ""))
})
```