我似乎花了很多时间从文件,数据库或其他东西创建一个数据框,然后将每一列转换成我想要的类型(数字,因子,字符等)。有没有一种方法可以一步一步做到这一点,可能是通过提供一个类型为vector的方法?
foo<-data.frame(x=c(1:10),
y=c("red", "red", "red", "blue", "blue",
"blue", "yellow", "yellow", "yellow",
"green"),
z=Sys.Date()+c(1:10))
foo$x<-as.character(foo$x)
foo$y<-as.character(foo$y)
foo$z<-as.numeric(foo$z)
代替最后三个命令,我想做类似的事情
foo<-convert.magic(foo, c(character, character, numeric))
Edit有关此基本思想的一些简化和扩展,请参见this相关问题。
我对[[0]的布兰登答案的评论:
switch
对于真正的大数据帧,您可能需要使用convert.magic <- function(obj,types){
for (i in 1:length(obj)){
FUN <- switch(types[i],character = as.character,
numeric = as.numeric,
factor = as.factor)
obj[,i] <- FUN(obj[,i])
}
obj
}
out <- convert.magic(foo,c('character','character','numeric'))
> str(out)
'data.frame': 10 obs. of 3 variables:
$ x: chr "1" "2" "3" "4" ...
$ y: chr "red" "red" "red" "blue" ...
$ z: num 15254 15255 15256 15257 15258 ...
而不是lapply
循环:
for
[执行此操作时,请注意R中强制数据的某些复杂性。例如,从因数转换为数字通常涉及convert.magic1 <- function(obj,types){
out <- lapply(1:length(obj),FUN = function(i){FUN1 <- switch(types[i],character = as.character,numeric = as.numeric,factor = as.factor); FUN1(obj[,i])})
names(out) <- colnames(obj)
as.data.frame(out,stringsAsFactors = FALSE)
}
。另外,请注意as.numeric(as.character(...))
和data.frame()
的将字符转换为因数的默认行为。
使用foo[] <- lapply(foo, readr::parse_guess)
#'data.frame': 10 obs. of 3 variables:
# $ x: num 1 2 3 4 5 6 7 8 9 10
# $ y: chr "red" "red" "red" "blue" ...
# $ z: Date, format: "2019-08-12" "2019-08-13" "2019-08-14" "2019-08-15" ...
和foo <- transform(foo, x=as.character(x), y=as.character(y), z=as.numeric(z))
:
purrr
如果您想自动检测列的数据类型而不是手动指定(例如,在整理数据后等),则功能as.data.frame()
可能会有所帮助。
函数type.convert()
接受字符向量,并尝试确定所有元素的最佳类型(这意味着必须每列应用一次)。
type.convert()
因为我爱type.convert()
,所以我更喜欢:
df[] <- lapply(df, function(x) type.convert(as.character(x)))
我发现我也经常遇到这个问题。这是关于如何导入数据的。所有的read ...()函数都有某种类型的选项,用于指定不将字符串转换为因数。这意味着文本字符串将保持字符状态,而看起来像数字的事物将保持数字状态。当您的元素为空而不是不适用时,就会出现问题。但同样,na.strings = c(“”,...)也应解决该问题。首先,我将仔细研究您的导入过程并进行相应的调整。
但是您总是可以创建一个函数并通过该字符串。
dplyr
我知道我回答的时间很晚,但是将循环与attributes函数一起使用是解决您的问题的简单方法。
library(dplyr)
df <- df %>% mutate_all(funs(type.convert(as.character(.))))
我只是用RSQLite提取方法遇到了类似的事情……结果以原子数据类型返回。就我而言,这是一个日期时间戳,这使我感到沮丧。我发现convert.magic <- function(x, y=NA) {
for(i in 1:length(y)) {
if (y[i] == "numeric") {
x[i] <- as.numeric(x[[i]])
}
if (y[i] == "character")
x[i] <- as.character(x[[i]])
}
return(x)
}
foo <- convert.magic(foo, c("character", "character", "numeric"))
> str(foo)
'data.frame': 10 obs. of 3 variables:
$ x: chr "1" "2" "3" "4" ...
$ y: chr "red" "red" "red" "blue" ...
$ z: num 15254 15255 15256 15257 15258 ...
函数对于帮助使names <- c("x", "y", "z")
chclass <- c("character", "character", "numeric")
for (i in (1:length(names))) {
attributes(foo[, names[i]])$class <- chclass[i]
}
正常工作非常有用。这是我的小例子。
setAs
@ joran的答案的补充,其中as
不会在因子到数字的转换中保留数值:
##data.frame conversion function
convert.magic2 <- function(df,classes){
out <- lapply(1:length(classes),
FUN = function(classIndex){as(df[,classIndex],classes[classIndex])})
names(out) <- colnames(df)
return(data.frame(out))
}
##small example case
tmp.df <- data.frame('dt'=c("2013-09-02 09:35:06", "2013-09-02 09:38:24", "2013-09-02 09:38:42", "2013-09-02 09:38:42"),
'v'=c('1','2','3','4'),
stringsAsFactors=FALSE)
classes=c('POSIXct','numeric')
str(tmp.df)
#confirm that it has character datatype columns
## 'data.frame': 4 obs. of 2 variables:
## $ dt: chr "2013-09-02 09:35:06" "2013-09-02 09:38:24" "2013-09-02 09:38:42" "2013-09-02 09:38:42"
## $ v : chr "1" "2" "3" "4"
##is the dt column coerceable to POSIXct?
canCoerce(tmp.df$dt,"POSIXct")
## [1] FALSE
##and the conver.magic2 function fails also:
tmp.df.n <- convert.magic2(tmp.df,classes)
## Error in as(df[, classIndex], classes[classIndex]) :
## no method or default for coercing “character” to “POSIXct”
##ittle reading reveals the setAS function
setAs('character', 'POSIXct', function(from){return(as.POSIXct(from))})
##better answer for canCoerce
canCoerce(tmp.df$dt,"POSIXct")
## [1] TRUE
##better answer from conver.magic2
tmp.df.n <- convert.magic2(tmp.df,classes)
##column datatypes converted as I would like them!
str(tmp.df.n)
## 'data.frame': 4 obs. of 2 variables:
## $ dt: POSIXct, format: "2013-09-02 09:35:06" "2013-09-02 09:38:24" "2013-09-02 09:38:42" "2013-09-02 09:38:42"
## $ v : num 1 2 3 4
以下应保留数值:
convert.magic
一个稍微简单的data.table解决方案,但是如果要更改为许多不同的列类型,则将需要一些步骤。
convert.magic <- function(obj,types){
out <- lapply(1:length(obj),FUN = function(i){FUN1 <- switch(types[i],
character = as.character,numeric = as.numeric,factor = as.factor); FUN1(obj[,i])})
names(out) <- colnames(obj)
as.data.frame(out,stringsAsFactors = FALSE)
}
foo<-data.frame(x=c(1:10),
y=c("red", "red", "red", "blue", "blue",
"blue", "yellow", "yellow", "yellow",
"green"),
z=Sys.Date()+c(1:10))
foo$x<-as.character(foo$x)
foo$y<-as.character(foo$y)
foo$z<-as.numeric(foo$z)
str(foo)
# 'data.frame': 10 obs. of 3 variables:
# $ x: chr "1" "2" "3" "4" ...
# $ y: chr "red" "red" "red" "blue" ...
# $ z: num 16777 16778 16779 16780 16781 ...
foo.factors <- convert.magic(foo, rep("factor", 3))
str(foo.factors) # all factors
foo.numeric.not.preserved <- convert.magic(foo.factors, c("numeric", "character", "numeric"))
str(foo.numeric.not.preserved)
# 'data.frame': 10 obs. of 3 variables:
# $ x: num 1 3 4 5 6 7 8 9 10 2
# $ y: chr "red" "red" "red" "blue" ...
# $ z: num 1 2 3 4 5 6 7 8 9 10
# z comes out as 1 2 3...
这会将## as.numeric function that preserves numeric values when converting factor to numeric
as.numeric.mod <- function(x) {
if(is.factor(x))
as.numeric(levels(x))[x]
else
as.numeric(x)
}
## The same than in @joran's answer, except for as.numeric.mod
convert.magic <- function(obj,types){
out <- lapply(1:length(obj),FUN = function(i){FUN1 <- switch(types[i],
character = as.character,numeric = as.numeric.mod, factor = as.factor); FUN1(obj[,i])})
names(out) <- colnames(obj)
as.data.frame(out,stringsAsFactors = FALSE)
}
foo.numeric <- convert.magic(foo.factors, c("numeric", "character", "numeric"))
str(foo.numeric)
# 'data.frame': 10 obs. of 3 variables:
# $ x: num 1 2 3 4 5 6 7 8 9 10
# $ y: chr "red" "red" "red" "blue" ...
# $ z: num 16777 16778 16779 16780 16781 ...
# z comes out with the correct numeric values
中指定的列以外的所有列更改为数字(或在dt <- data.table( x=c(1:10), y=c(10:20), z=c(10:20), name=letters[1:10])
dt <- dt[, lapply(.SD, as.numeric), by= name]
中设置的任何列]
类似于by
,也有lapply
无需指定即可将数据帧转换为适当的类
type.convert(foo, as.is = TRUE)
如果将所有列都保留为字符,我们也可以使用readr::type_convert
,它将自动将数据框转换为正确的类。考虑修改后的数据框
readr::type_convert(foo)
在每列上应用readr::parse_guess
foo <- data.frame(x = as.character(1:10),
y = c("red", "red", "red", "blue", "blue", "blue", "yellow",
"yellow", "yellow", "green"),
z = as.character(Sys.Date()+c(1:10)), stringsAsFactors = FALSE)
str(foo)
#'data.frame': 10 obs. of 3 variables:
# $ x: chr "1" "2" "3" "4" ...
# $ y: chr "red" "red" "red" "blue" ...
# $ z: chr "2019-08-12" "2019-08-13" "2019-08-14" "2019-08-15" ...
转换似乎就是您要描述的内容:
parse_guess