Using Loop to extract climatic information from Library in R

Question

I have a quite large database. I need to extract climate information from the "Nasapower" Library.

My reduced dataset looks like this:

api_decimal<- data.frame (
    AP_COD = c("LOM_A", "LOM_L", "LOM_M", "LOM_LA", "LOM_CO"),
    LAT_DEC = c(25.628,
                25.641,
                25.415,
                25.435,
                25.424),
    LONG_DEC = c(7.300,
                 7.314,
                 7.450,
                 7.449,
                 7.443)
    
  )

api_decimal$site <- paste(api_decimal$LAT_DEC, ",", api_decimal$LONG_DEC)

I tried to make a loop to extract the "daily" "Temperature (TM2)" information for the years 2014 to 2020 for all sites (latitude, longitude), but the loop doesn't work:

years <- c("2014", "2015", "2016", "2017", "2018", "2019")
for (i in seq_along(years)){
  year <- years[[i]]
  
  for(j in seq_along(nrow(api_decimal$site))) {
    sites <- as.numeric(api_decimal$site[j, ])
    ag_d <- get_power(
      community = "ag",
      lonlat = sites,
      pars = "T2M",
      dates = years,
      temporal_api = "daily"
    )
  }
}

Any suggestions?

Thank in advance

Answer 1

There were a few problems with he code. First, since nrow(api_decimal$site) is NULL, seq_along(nrow(api_decimal$site)) evaluates to logical(0). Instead, you want seq_along(api_decimal$site). There were a couple of problems with your call to get_power(). First, the lonlat argument is meant to be a vector of length two. The way you're doing it in the code creates a single string with two decimals separated by a comma. When you turn this into a numeric value, it doesn't make two numeric values, it only makes a single NA value. Instead, you can just use the longitude and latitude coordinates that are already in the data. Finally, the dates argument wants length 2 character vector giving the start and end dates in YYYY-MM-DD format. You could make this by pasting your year variable to "-01-01" for the start and to "-12-31" for the end.

If the loop had run, you would have also been overwriting ag_d with every iteration. You could solve that by initializing ag_d outside the loop and then using rbind(ag_d, new_result) to accumulate the results as you move through the iterations of the loop. This code should work:

library(nasapower)
api_decimal<- data.frame (
  AP_COD = c("LOM_A", "LOM_L", "LOM_M", "LOM_LA", "LOM_CO"),
  LAT_DEC = c(25.628,
              25.641,
              25.415,
              25.435,
              25.424),
  LONG_DEC = c(7.300,
               7.314,
               7.450,
               7.449,
               7.443)
  
)

years <- c("2014", "2015", "2016", "2017", "2018", "2019")
ag_d <- NULL
for (i in seq_along(years)){
  year <- years[[i]]
  for(j in seq_along(api_decimal$LONG_DEC)) {
    ag_d <- rbind(ag_d, 
                  get_power(
                    community = "ag",
                    lonlat = c(api_decimal$LONG_DEC[j], api_decimal$LAT_DEC[j]),
                    pars = "T2M",
                    dates = c(paste0(years[i], "-01-01"), 
                              paste0(years[i], "-12-31")),
                    temporal_api = "daily"
    ))
  }
}