Forcing Visualizations in R to Have Only 2 Decimal Points

Question

I am trying to make an interactive Leaflet map in R. I have a shapefile that looks something like this:

# my_shapefile

Simple feature collection with 6 features and 5 fields
geometry type: MULTIPOLYGON
dimensions : xy
bbox: xmin ... y min ... xmax ... ymax...
CRS: EPSG:  4326

ID: A, B, A
Geometry : MULTIPOLYGON ((( 55.23, -71.22 ....
value :  0.12, 0.15, 0.13

I made the following map:

#taken from here: https://cengel.github.io/R-spatial/mapping.html
library(sf)
library(leaflet)
library(classInt)
library(RColorBrewer)

sf <- sf::st_read("my_shapefile.shp", options = "ENCODING-WINDOWS-1252")

#note: "value" comes from another file that I merged to the shapefile

st_trans <- st_transform(sf, 4326)

breaks_qt <- classIntervals(sf$value, n=7, style "quantile")

pal_fun <- colorQuantile("YlOrRd", NULL, n = 5)

# here is the problem I think

p_popup <- paste0("<strong> Value : </strong>", sf$value)

leaflet(st_trans) %>%
addPolygons(
stroke = FALSE,
fillColor = ~ pal_fun(value),
fillOpacity = 0.8, smoothFactor = 0.5,
popup = p_popup,
group = "my_group") %>%
addTiles(group = "OSM") %>%
addProviderTiles("CartoDB.DarkMatter", group = "Carto") %>%
addLegend("bottomright", 
colors = brewer.pal(7, "YlOrRd"),
labels = paste0("up to ", format(breaks_qt$brks[-1], digits = 2)),
title = 'my legend') %>%
addLayersControl(baseGroups = c("OSM", "Carto"), overlapGroups = c("my_group"))

This map runs fine, the problem is that when I move the mouse over the map, the popup for "value" appears with many decimal points - I would like to restrict the number of decimal points to only two. The "value" variable was calculated by dividing two variables together, so I suspect that the many decimal points are coming from this.

I first tried to turn off the decimal points using the code found here (Formatting Decimal places in R), but this did not work:

#did not work
options(digits=2)

Next, I tried to manually keep only two decimal points, but this also did not work (i.e. the visualization is still displaying many decimal points):

# did not work
sf$value = substr(sf$value, 1,4)

Finally, I found this post here (R Leaflet Legend: colorBin- removing decimals in between breaks) and tried to follow this advice for restricting the number of decimal points:

#did not work

leaflet(st_trans) %>%
addPolygons(
stroke = FALSE,
fillColor = ~ pal_fun(value),
fillOpacity = 0.8, smoothFactor = 0.5,
popup = p_popup,
group = "my_group") %>%
addTiles(group = "OSM") %>%
addProviderTiles("CartoDB.DarkMatter", group = "Carto") %>%
addLegend("bottomright", labFormat = labelFormat(prefix = '', suffix = '', between = ' – ', digits = 3, big.mark = ',', transform = identity),
colors = brewer.pal(7, "YlOrRd"),
labels = paste0("up to ", format(breaks_qt$brks[-1], digits = 2)),
title = 'my legend') %>%
addLayersControl(baseGroups = c("OSM", "Carto"), overlapGroups = c("my_group"))

• Can someone please show me what I am doing wrong and what I can do to ensure that the popup in the leaflet map only contains two decimal points?

Answer 1

Are you able to use the format() approach listed as an answer in this thread:

Formatting Decimal places in R

x = 1.20000
format(round(x, 2), nsmall = 2)
[1] "1.20"

where x is your input of choice.

Answer 2

Use one of the functions for formatting decimals to construct your popups.

Minimal example:

sf = st_as_sf(data.frame(x=1:10, y=1:10, value=runif(10)), crs=4326, coords=1:2)
p_popup <- paste0("<strong> Value : </strong>", sprintf("%.2f", sf$value))
leaflet(sf) %>% addMarkers( popup=p_popup)

The values are:

> sf$value
 [1] 0.3315254 0.9618285 0.8060112 0.2322543 0.7385210 0.6962690 0.8464728
 [8] 0.7286911 0.6193918 0.1502202

and the popups are like this:

Note 0.7385210 is rounded to 0.74. Adjust format string to suit your application.