Subset a dataframe using a array created by itself in R

Question

Sorry about that I don't how to describe my question in Title.

My problem is that

I have a dataframe as below

| id | content | created_at          |
|----|---------|---------------------|
| 1  | hello   | 2014-12-10 00:00:00 |
| 2  | world   | 2013-11-11 00:00:00 |
| 3  | oh~no   | 2012-10-10 00:00:00 |
| 4  | helpme  | 2011-09-11 00:00:00 |

I want to subset this frame by time interval

for example:

subset: 2011 - 2012

| 4 | helpme | 2011-09-11 00:00:00 |
subset: 2012 - 2013

| 3 | oh~no | 2012-10-10 00:00:00 |
subset: 2013 - 2014

| 2 | world | 2013-11-11 00:00:00 |
subset: 2014 - 2015

| 1 | hello | 2014-12-10 00:00:00 |

Below is how I try to resolve this problem

I try to create a true,false array and do in each row

ifelse( 

 difftime(DF$created_at,as.Date(ISOdate(seq(2004,2014),1,1))) >= 0 & 

 difftime(DF$created_at,as.Date(ISOdate(seq(2005,2015),1,1))) < 0

 , assign_to_subset_X, do_nothing)

but....

I don't think this is a good idea especially I already use R....

then I find some solutions such as apply

  apply(DF, 2, do_a_function_to_subset)

but I still have no idea to write this function

please give me a hint.

johannes johannes · Accepted Answer · 2014-12-10T12:11:49

Here is one possible solution

library(lubridate)
df <- read.table(textConnection("  id | content | created_at          
 1  | hello   | 2014-12-10 00:00:00 
 2  | world   | 2013-11-11 00:00:00 
 3  | oh~no   | 2012-10-10 00:00:00 
 4  | helpme  | 2011-09-11 00:00:00 "), header=TRUE, sep="|")


df$ts <- ymd_hms(df$created_at)

## create an interval
myInt <- ymd("2011-01-01") %--% ymd("2011-12-31")
df[df$ts %within% myInt, ]

Subset a dataframe using a array created by itself in R

1 Answers