How to name objects within a for loop in r using the values in the sequence as names

Question

Below is my code so far, which doesn't work. I have 7 dataframes that each contain information about one pollutant (named in pollutant_long_name). Each of these dataframes is called, for example, national_tier1_Nitrogen Oxides or national_tier1_Ammonia. I've been trying to use the paste0 function to use the values in my for loop sequence within the for loop, but it doesn't seem to be working. The first error I got is

Error: unexpected '=' in: " dplyr::group_by( inv_sector ) %>%
dplyr::summarise( paste0( "NEI_emissions_", pollutant_name, "_2011" ) ="

Basically, my end goal is the have 7 dataframes called total_2011_pollutant name that I'll then leftjoin to make a dataframe containing all 7 pollutants.

pollutant_long_name <- c( "Nitrogen Oxides", "Sulfur Dioxide", "Carbon Monoxide", "Volatile Organic Compounds",
                          "PM2.5 Filterable", "PM10 Filterable", "Ammonia" )
for( n in pollutant_long_name ){
  pollutant_name <- paste0( n )
#===================================================================================NOX
NEI_2011 %>%
  dplyr::left_join( CEDS_to_EPA_rename, by = c( "CEDS_Sector" ) ) %>%
  dplyr::filter( pollutant == pollutant_name ) %>%
  dplyr::group_by( inv_sector ) %>%
  dplyr::summarise( paste0( "NEI_emissions_", pollutant_name, "_2011" ) = sum( emissions/1000 ) ) %>%
  round_df( digits = 0 )-> NEI_2011_emissions

paste0( "national_tier1_", pollutant_name ) %>%
  dplyr::select( c(Source.Category, X2011) ) %>%
  dplyr::rename( inv_sector = Source.Category ) %>%
  dplyr::mutate( X2011 = gsub( ",", "", X2011 ) ) %>%
  dplyr::mutate( X2011 = as.numeric(as.character( X2011 ) ) ) %>%
  dplyr::rename( national_2011_NOX = X2011 )-> paste0( "national_2011_", pollutant_name )

NEI_2011_emissions %>%
  dplyr::left_join( paste0( "national_2011_", pollutant_name ), by = c( "inv_sector" ) ) -> paste0( "total_2011_", pollutant_name )
paste0( "total_2011_", pollutant_name )[is.na(paste0( "total_2011_", pollutant_name ))] <- 0
}

akrun · Accepted Answer · 2020-07-07 21:25:23Z

1

If we use string on the lhs of =, it wouldn't work, instead we can make use := while evaluating the string with (!!)

library(dplyr)
NEI_2011 %>%
  dplyr::left_join( CEDS_to_EPA_rename, by = c( "CEDS_Sector" ) ) %>%
  dplyr::filter( pollutant == pollutant_name ) %>%
  dplyr::group_by( inv_sector ) %>%
  dplyr::summarise( !!paste0( "NEI_emissions_",  ## changed
       pollutant_name, "_2011" ) := sum( emissions/1000 ) ) %>% ## changed
  round_df( digits = 0 )-> NEI_2011_emissions

For the second chunk to create the object name with paste, it is still a string. If we need to get the value of the string object then use get (for multiple objects use mget - returns a list of object values). To assign the output to an object, use assign

assign(paste0( "national_2011_", pollutant_name ), 
   get(paste0( "national_tier1_", pollutant_name )) %>%
   dplyr::select( c(Source.Category, X2011) ) %>%
   dplyr::rename( inv_sector = Source.Category ) %>%
   dplyr::mutate( X2011 = gsub( ",", "", X2011 ) ) %>%
   dplyr::mutate( X2011 = as.numeric(as.character( X2011 ) ) ) %>%
   dplyr::rename( national_2011_NOX = X2011 ))

Generally, it is not really needed to assign multiple objects in the global environment. We could create a single list to store the output of different values

edited Jul 7, 2020 at 21:25

answered Jul 7, 2020 at 21:02

akrun

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2 Comments

Maridee Weber Over a year ago

thank you! I'm now getting Error in UseMethod("select_") : no applicable method for 'select_' applied to an object of class "character" for the second chunk there, all columns are factors, which I didn't think would matter for select and rename to work?

akrun Over a year ago

@MarideeWeber. If you meant paste0( "national_tier1_", pollutant_name ) %>% it is a string object, you need get(paste0( "national_tier1_", pollutant_name )) to get the values of that object

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