Using rescale function after grouping data in R

Question

I have a data frame that measures vertical movement of multiple objects with unique ID's. I want to rescale the X,Y coordinates from pixels to cm by using the rescale package. Each object has a minimum value of 0cm and maximum of 12.5cm, but the pixel lengths are all different because some objects were closer and some further away. I wanted to group my data by unique ID, and then rescale between 0 and 12.5cm. This is the code I used:

Data <- Data %>%
  group_by(ID) %>%
  rescale(Data$Y, to = c(0, 12.5), from = range(Data$Y, na.rm = TRUE, finite = TRUE))

I think I am grouping my data wrong, because I keep getting the following error:

Error in UseMethod("rescale") : 
  no applicable method for 'rescale' applied to an object of class "c('grouped_df', 'tbl_df', 'tbl', 'data.frame')"

Any suggestions for how to format this?

`group_by` only works with functions that are built to work with it---which is mostly `dplyr` functions. — Gregor Thomas, May 04 '20 at 18:20

score 0 · Accepted Answer · answered May 04 '20 at 18:15

Assuming that the rescale is from scales, after the group_by, rescale it within mutate by just specifying the column name without the Data$. Using Data$ will extract the entire column instead of the values for each group

library(dplyr)
library(scales)
Data %>%
   group_by(ID) %>%
   mutate(Y = rescale(Y, to = c(0, 12.5), 
       from = range(Y, na.rm = TRUE, finite = TRUE)))

Using a reproducible example with mtcars

data(mtcars)
mtcars %>% 
    group_by(cyl) %>%
    mutate(mpg = rescale(mpg, to = c(0, 12.5), 
          from = range(mpg, na.rm = TRUE, finite = TRUE)))

Using rescale function after grouping data in R

1 Answers1