Write data frame to multiple csv's in R

Question

I have the below data frame which contains infomation about different states.

long=c(-106.61291,-106.61291,-106.61291,-81.97224,-81.97224,-81.97224,-84.4277,-84.4277,-84.4277)
lat=c(35.04333,35.04333,35.04333,33.37378,33.37378,33.37378,33.64073,33.64073,33.64073)
city=c("Albuquerque","Albuquerque","Albuquerque","Augusta","Augusta","Augusta","Atlanta","Atlanta","Atlanta")
date=c("2017-08-22","2017-08-23","2017-09-24","2017-09-28","2017-10-24","2017-09-22","2017-11-12","2017-010-14","2017-09-03")
value=c(12,10.8,18.3,12.4,43,21,12,32.1,14)

df<-data.frame(long,lat,city,date,value)

Problem :I want to write each city information in individual csv's. And each csv should look like below. Final output:

Albuquerque.csv
       long      lat        city       date value
1 -106.6129 35.04333 Albuquerque 2017-08-22  12.0
2 -106.6129 35.04333 Albuquerque 2017-08-23  10.8
3 -106.6129 35.04333 Albuquerque 2017-09-24  18.3

Augusta.csv
      long      lat    city       date value
1 -81.97224 33.37378 Augusta 2017-09-28  12.4
2 -81.97224 33.37378 Augusta 2017-10-24  43.0
3 -81.97224 33.37378 Augusta 2017-09-22  21.0

Atlanta.csv
      long      lat    city        date value
1 -84.4277 33.64073 Atlanta  2017-11-12  12.0
2 -84.4277 33.64073 Atlanta 2017-010-14  32.1
3 -84.4277 33.64073 Atlanta  2017-09-03  14.0

Thanks in advance!

Answer 1

# Split dataframe by city
split_df <- split(df, list(df$city))

# Write out separate CSV for each city
for (city in names(split_df)) {
    write.csv(split_df[[city]], paste0(city, ".csv"))
}

Answer 2

long=c(-106.61291,-106.61291,-106.61291,-81.97224,-81.97224,-81.97224,-84.4277,-84.4277,-84.4277)
lat=c(35.04333,35.04333,35.04333,33.37378,33.37378,33.37378,33.64073,33.64073,33.64073)  
city=c("Albuquerque","Albuquerque","Albuquerque","Augusta","Augusta","Augusta","Atlanta","Atlanta","Atlanta")
date=c("2017-08-22","2017-08-23","2017-09-24","2017-09-28","2017-10-24","2017-09-22","2017-11-12","2017-010-14","2017-09-03")
value=c(12,10.8,18.3,12.4,43,21,12,32.1,14)

df<-data.frame(long,lat,city,date,value)

dflist <- split(df , f = df$city)

sapply(names(dflist), 
 function (x) write.csv(dflist[[x]], file=paste(x, "csv", sep=".") )   )

Answer 3

There's a few different ways of doing this but a very quick approach to do this for all your cities at once is to take advantage of the apply family of functions in base R - specifically lapply .

long=c(-106.61291,-106.61291,-106.61291,-81.97224,-81.97224,-81.97224,-84.4277,-84.4277,-84.4277)
lat=c(35.04333,35.04333,35.04333,33.37378,33.37378,33.37378,33.64073,33.64073,33.64073)
city=c("Albuquerque","Albuquerque","Albuquerque","Augusta","Augusta","Augusta","Atlanta","Atlanta","Atlanta")
date=c("2017-08-22","2017-08-23","2017-09-24","2017-09-28","2017-10-24","2017-09-22","2017-11-12","2017-010-14","2017-09-03")
value=c(12,10.8,18.3,12.4,43,21,12,32.1,14)

df<-data.frame(long,lat,city,date,value)

# create a convenience function to split your data and export to csv
split_into_csv <- function(x) {
tmp <- df[df$city == x,]
write.csv(tmp, file = paste0(x,".csv"))}

# Apply split_into_csv over elements of list with lapply
lapply(levels(df$city), split_into_csv)
# Check output in director
dir()
[1] "Albuquerque.csv" "Atlanta.csv"     "Augusta.csv"  

Answer 4

You can do this with base R or with the dplyr package.

dplyr way:

dplyr::filter(df, city == 'Albuquerque') %>% write.csv(file = 'Albuquerque.csv', row.names = FALSE)
dplyr::filter(df, city == 'Augusta') %>% write.csv(file = 'Augusta.csv', row.names = FALSE)
dplyr::filter(df, city == 'Atlanta') %>% write.csv(file = 'Atlanta.csv', row.names = FALSE)

base R:

write.csv(df[df$city == 'Albuquerque', ], file = 'Albuquerque.csv', row.names = FALSE)
write.csv(df[df$city == 'Augusta', ], file = 'Augusta.csv', row.names = FALSE)
write.csv(df[df$city == 'Atlanta', ], file = 'Atlanta.csv', row.names = FALSE)

You can use a for loop if you start getting more cities.

for (city in c('Albuquerque', 'Augusta', 'Atlanta')) {
  write.csv(df[df$city == city, ], file = paste0(city, '.csv'))
}