Download, Plot map, and extract data in R - r

Question

I downloaded a monthly data from [NASA data][1] and saved in .txt and .asc format. I am trying to plot and extract the data from the ASCII file, but unfortunately I am unable to do so. I tried the following:
1.
infile <- "OMI/L3feb09.txt"
data <- as.matrix(read.table(infile, skip = 3, header = FALSE, sep = "\t"))
data[data == -9999] = NA
rr <- raster(data, crs = "+init=epsg:4326")
extent(rr) = c(179.375, 179.375+1.25*288, -59.5, -59.5+1*120)
Tried to extract for australia
adm <- getData("GADM", country="AUS", level=1)
rr = mask(rr, adm)
plot(rr)
library(rgdal)
r = raster("OMI/L3feb09.txt")
plot(r)
library(raster)
r = raster("OMI/L3feb09.txt")
plot(r)
4.Also tried,
df1 <- read.table("OMI/L3feb09.txt", skip = 11, header = FALSE, sep = "\t")
Tried the following from
Stackoverflow link 1
Stackoverflow link 2
The problem is there are strings in the file in between number, such as "lat = -55.5"
Appreciate any kind of help. Thank you
[2]: https://stackoverflow.com/questions/42064943/opening-an-ascii-file-using-r

Answer 1

So, I downloaded one file and played around with it! It is not the best solution, however, I hope it can give you an idea.
library(stringr)
# read data
data<-read.csv("L3_tropo_ozone_column_oct04",header = FALSE, skip = 3,sep = "")
# this "" will seperate lat = -59.5 to 3 rows, and will be easier to remove.
#Also each row in the data frame constrained by 2 rows of "lat", represents #data on the later "lat".
lat_index<-which(data[,1]=="lat")
#you need the last row that contains data not "lat string
lat_index<-lat_index-1
#define an empty array for results.
result<-array(NA, dim = c(120,288),dimnames = list(lat=seq(-59.5,59.5,1),
lon=seq(-179.375,179.375,1.25)))
I assumed data -on 3 three digits- on each latituide is dividable by 3 resulting in 288, which equals the lon grid number. Correct me if I'm wrong.
# function to split a string into a vector in which each string has three letter/numbers
split_n_parts<-function(input_string,n){
# dislove it to many elements or by number
input_string_1<-unlist(str_extract_all(input_string,boundary("character")))
output_string<-vector(length = length(input_string_1)/n)
for ( x in 1:length(output_string)){
output_string[x]<-paste0(input_string_1[c(x*3-2)],
input_string_1[c(x*3-1)],
input_string_1[c(x*3)])
}
return(as.numeric(output_string))
}
Here, the code loops, collects, write each lat data in the result array
# loop over rows constrainted by 2 lats, process it and assign to an array
for (i in 1:length(lat_index)){
if(i ==1){
for(j in 1:lat_index[i]){
if(j==1){
row_j<-paste0(data[j,])
}else{
row_j<-paste0(row_j,data[j,])
}
}
}else{
ii<-i-1
lower_limit<-lat_index[ii]+4
upper_limit<-lat_index[i]
for(j in lower_limit:upper_limit){
if(j==lower_limit){
row_j<-paste0(data[j,])
}else{
row_j<-paste0(row_j,data[j,])
}
}
}
result[i,]<-split_n_parts(row_j,3)
}
Here, is the final array and image
#plot as image
image(result)
EDIT: To continue the solution and put the end-result:
# because data is IN DOBSON UNITS X 10
result<-result/10
#melt to datafrome
library(plyr)
result_df<-adply(result, c(1,2))
result_df$lat<-as.numeric(as.character(result_df$lat))
result_df$lon<-as.numeric(as.character(result_df$lon))
# plotting
library(maps)
library(ggplot2)
library(tidyverse)
world_map <- map_data("world")
#colors
jet.colors <-colorRampPalette(c("white", "cyan", "#7FFF7F", "yellow", "#FF7F00", "red", "#7F0000"))
ggplot() +
geom_raster(data=result_df,aes(fill=V1,x=lon,y=lat))+
geom_polygon(data = world_map, aes(x = long, y = lat, group = group),
fill=NA, colour = "black")+
scale_x_continuous(expand = c(0, 0)) +
scale_y_continuous(expand = c(0, 0))+
scale_fill_gradientn(colors = jet.colors(7))