CODEWITHSUNDEEP
rloopsgisapply
John L. Godlee
John L. Godlee

Reputation: 601

areaPolygon() on list of data frames R

packages:

library(geosphere)
library(dplyr)

I have a list of data frames like this:

df_list:

[[1]]
  name X1 X2
1    A  1  1
2    A  1  2
3    A  2  2
4    A  2  1

[[2]]
  name X1 X2
1    B  1  1
2    B  1  2
3    B  2  2
4    B  2  1

[[3]]
  name X1 X2
1    C  1  1
2    C  1  2
3    C  2  2
4    C  2  1

I want to loop through each data frame in the list and calculate the area of the polygon the dataframe represents using areaPolygon() from the geosphere package. I can do this for one data frame like this:

name <- c("A","A","A","A")
X1 <- c(1,1,2,2)
X2 <- c(1,2,2,1)
df <- data.frame(name, X1, X2)

areaPolygon(df[,2:3])

I tried doing this with pipes by concatenating the list of data frames into one dataframe and grouping by name:

df_list_con <- do.call(rbind, df_list)
area <- df_list_concat %>% group_by(name) %>% areaPolygon(.[,2:3])

but it didn't work, giving the error message:

Error in (function (classes, fdef, mtable)  : 
unable to find an inherited method for function ‘areaPolygon’ for signature ‘"grouped_df"’

Can I do this using mapply or lapply? I wouldn't know how to do it.

Upvotes: 0

Views: 97

Answers (1)

Iaroslav Domin
Iaroslav Domin

Reputation: 2718

Grouping with group_by is a dplyr-thing, to be used by dplyr functions such as summarise and you shouldn't expect in general that functions from other packages will understand it.

What you need here is:

df_list_concat %>% 
    group_by(name) %>% 
    summarise(area = areaPolygon(cbind(X1, X2)))

Upvotes: 1

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