How can I write parts of a list into one data frame?

问题

I want to write a single df with the freq of 150 raster objects (partly answered in: Count freq of multiple raster objects in R)

I have created a list of all the raster files with

spatial.tools::list.raster.files() and then called

lapply(ls$raster,freq)

Now I have a list containing 150 entries that contain a freq matrix for every raster file.

I am only interested in $Band.1[,"count"]) however. For a single entry of the list I can create a df for counts with

as.data.frame(all[[1]]$Band.1[,"count"])

My question is: How can I write $Band.1[,"count"] for all of the 150 in the list into a single df in one go???

回答1:

I see you're new here. Others will have an easier time answering your question if you can make your question reproducible -- check out this post on how to make a great reproducible example. That being said, using your other question, this should likely get you what you need:

library(tidyverse)

list_of_results <- lapply(ls$raster,freq)

df_of_results <- 
  list_of_results %>%
  map_df(~ data.frame(.))

df_of_results$count

If the tidyverse and purrr::map functions aren't your thing, you could also do something like:

results <- unlist(lapply(list_of_results, function(x) x[, c("count")]))

来源：https://stackoverflow.com/questions/52388444/how-can-i-write-parts-of-a-list-into-one-data-frame