How To Repeat Code w/ Variables

[HABSaremyjam]

Hello,

I am using the USGS dataRetrieval package to get some TP data for specific USGS site numbers. Here is the code that I am using the get the data and restructure it. What I want to do is create some way for R to repeat this code for each of the station numbers so that I don't have to copy/paste the code and manually change the variables.

In this example, the variable I want to change is siteNumber. Is there a way to do this?

#Store station numbers
Mil <- "04087170"
StJ <- "04101500"
Kal <- "04108660"
Gra <- "04119400"
Mus <- "04121970"
#store parameter codes
TP <- "00665"
Q <- "00060"

install.packages("dataRetrieval")
library("dataRetrieval")
Mil.TP <- readNWISqw(siteNumber = Mil, parameterCd=TP)
Mil.TP <- Mil.TP[c("site_no", "sample_dt", "result_va")]
names(Mil.TP)[names(Mil.TP) == "site_no"] <- "Site_Number"
names(Mil.TP)[names(Mil.TP) == "sample_dt"] <- "Sample_Date"
names(Mil.TP)[names(Mil.TP) == "result_va"] <- "TP_mg_per_L"

Any help on this would be greatly appreciated.

Thanks so much!!

[willwheels]

Here is code to get just the TP numbers. I am tempted to alter your base R code into a dplyr pipe, but didn't.

#install.packages("dataRetrieval")
library("dataRetrieval")
#> Warning: package 'dataRetrieval' was built under R version 4.0.4

site_nums <- c("04087170", "04101500", "04108660", "04119400", "04121970")
params <- c("00665", "00060")

get_one_site <- function(site_num) {
  TP <- readNWISqw(siteNumber = site_num, parameterCd = "00665")
  TP <- TP[c("site_no", "sample_dt", "parm_cd", "result_va")]
  names(TP)[names(TP) == "site_no"] <- "Site_Number"
  names(TP)[names(TP) == "sample_dt"] <- "Sample_Date"
  names(TP)[names(TP) == "parm_cd"] <- "Parameter_Code"
  names(TP)[names(TP) == "result_va"] <- "mg_per_L"
  
  
  return(TP)
  
}

combos_df <- tidyr::expand_grid(site_nums, params)

TPs <- purrr::map_dfr(combos_df$site_nums, get_one_site)

head(TPs)
#>   Site_Number Sample_Date Parameter_Code mg_per_L
#> 1    04087170  1994-03-29          00665     0.08
#> 2    04087170  1994-04-08          00665     0.06
#> 3    04087170  1994-04-19          00665     0.07
#> 4    04087170  1994-05-24          00665     0.04
#> 5    04087170  1994-06-14          00665     0.04
#> 6    04087170  1994-07-08          00665     0.10

^{Created on 2021-03-25 by the reprex package (v0.3.0)}

If you want to start pulling in parameters, you could use map2_dfr and pass the params column. I tried that but got an error (it appears that that "00060" discharge parameter is not reported for some sites, which threw and error in the dataRetrieval function that I don't have time to track down.