I have a number of dataframes in the global environment, let's call them a, b, and c .
Each of the dataframes has a column named start_time which needs to be converted into posix class, but I am looking for way to do this without writing out the same code for each dataframe. The code is:
a$start_time <- strptime(a$start_time, format = '%Y-%m-%d %H:%M:%S')
That would only convert the start_time in a
Using the dataframe names, how could one devise a way to loop over each of the dataframes and convert start_time to posix?
This attempt with lapply only works on the first dataframe...
ll <- list(a, b, c)
lapply(ll,function(df){
df$start_time <- strptime(df$start_time, format = '%Y-%m-%d %H:%M:%S')
})
Data: df1, df2, df3
df1 <- data.frame(start_time = seq(Sys.time(), Sys.time() + 100, 10))
df2 <- data.frame(start_time = seq(Sys.time(), Sys.time() + 100, 10))
df3 <- data.frame(start_time = seq(Sys.time(), Sys.time() + 100, 10))
# create a vector with names of the data frames
data_vec <- c('df1', 'df2', 'df3')
# loop through the data_vec and modify the start_time column
a1 <- lapply(data_vec, function( x ) {
x <- get( x )
x <- within(x, start_time <- strptime(start_time, format = '%Y-%m-%d %H:%M:%S') )
return( x )
})
# assign names to the modified data in a1
names(a1) <- data_vec
# list objects in global environment
ls()
# [1] "a1" "data_vec" "df1" "df2" "df3"
# remove df1, df2, df3 from global environment
rm(list = c('df1', 'df2', 'df3') )
# confirm the removal of data
ls()
# [1] "a1" "data_vec"
# assign the named list in a1 as data in global environment
list2env(a1, envir = .GlobalEnv)
# list objects in global environment and confirm that the data appeared again
ls()
# [1] "a1" "data_vec" "df1" "df2" "df3"
# output
head(df1)
# start_time
# 1 2017-03-03 22:49:54
# 2 2017-03-03 22:50:04
# 3 2017-03-03 22:50:14
# 4 2017-03-03 22:50:24
# 5 2017-03-03 22:50:34
# 6 2017-03-03 22:50:44
head(df2)
# start_time
# 1 2017-03-03 22:49:54
# 2 2017-03-03 22:50:04
# 3 2017-03-03 22:50:14
# 4 2017-03-03 22:50:24
# 5 2017-03-03 22:50:34
# 6 2017-03-03 22:50:44