Question

我有各种类型的数据框（数字，整数，日期，字符）。

我想将其子集化为格式为＆＃39;日期＆＃39;的列。我该怎么做呢？

mtcars$dates = '2015-05-05'
mtcars$dates = as.Date(mtcars$dates)

#filter just gives me:     newdf = mtcars$dates

Answer 1

我们可以使用console.log('planId: ' + planId + ' | ' + typeof planId); Output: planId: [ '576df16eed10c2fccbcbd60c' ] | object循环显示列，获取列的sapply，检查它是否是＆＃39;日期＆＃39;并使用该逻辑向量对列进行子集化。

class

Answer 2

使用Filter的另一种方式：

#make a function that checks for the Date class
is.Date <- function(x) inherits(x, 'Date')
#use Filter to filter the data.frame
Filter(is.Date, mtcars)

Answer 3

包 purrr 具有keep功能：

keep(mtcars, ~inherits(.x, "Date"))

~和.x编码允许在每列上使用inherits，而无需创建单独的函数或使用匿名函数。

Answer 4

07-Jul-2016 23:23:50.411 INFO [localhost-startStop-1] org.apache.catalina.core.ApplicationContext.log No Spring WebApplicationInitializer types detected on classpath 07-Jul-2016 23:24:03.676 INFO [localhost-startStop-1] org.apache.catalina.core.ApplicationContext.log Initializing Spring root WebApplicationContext 07-Jul-2016 23:24:04.696 SEVERE [localhost-startStop-1] org.apache.catalina.core.StandardContext.filterStart Exception starting filter sakai.request java.lang.NullPointerException at org.sakaiproject.util.RequestFilter.init(RequestFilter.java:649) at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:279) at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:260)允许您在数据框的列上使用谓词。只会选择谓词返回select_if的那些列：

TRUE

Answer 5

这应该有效：

data(mtcars)
mtcars$dates = '2015-05-05'
mtcars$dates = as.Date(mtcars$dates)
head(mtcars)

v=sapply(mtcars,class) #get the class of each column
datecol=names(v)[v=='Date'] # select the columns having date class
mtcars[datecol] #subset those columns.

选择日期字段

5 个答案: