转换多个数据帧的相同列

我在全球环境中有许多数据框，我们称它们为a,b和c。转换多个数据帧的相同列

每个数据帧都有一个名为start_time的列，需要将其转换为posix类，但我正在寻找方法来完成此操作，而无需为每个数据帧编写相同的代码。该代码是：

a$start_time <- strptime(a$start_time, format = '%Y-%m-%d %H:%M:%S')

这只会转换start_time在a

使用数据帧的名字，一个人如何可以设计一个地遍历每个dataframes和转换start_time POSIX的？

这种尝试用lapply只适用于第一个数据帧...

ll <- list(a, b, c) 
lapply(ll,function(df){ 
    df$start_time <- strptime(df$start_time, format = '%Y-%m-%d %H:%M:%S')   

})

来源

2017-03-04 the_darkside

数据：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

来源

2017-03-04 03:52:46 Sathish

有趣的工作流程，即工作 –

在OP的代码，并没有返回的数据集。因此，它基本上是

lapply(ll,function(df){ 
    df$start_time <- strptime(df$start_time, format = '%Y-%m-%d %H:%M:%S')   
    df 
})

但是，没有返回对象和匿名函数调用，transform是一个选项。另外，strptime也返回POSIXlt类。如果我们只需要POSIXct，使用as.POSIXct

lapply(ll, transform, start_time = as.POSIXct(start_time, format = '%Y-%m-%d %H:%M:%S'))

或者使其更为紧凑

library(lubridate) 
lapply(ll, transform, start_time = ymd_hms(start_time))

来源

2017-03-04 05:16:54 akrun

转换多个数据帧的相同列

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