R help - Aug 2017 - Comparing 2 dale columns

Dear R fellows,


I created a new column Date_flag to compare the dates of COL1 and COL2 using the
code
below. But it showed that 5/1/15 is greater than 6/1/2014 and 5/1/2015 greater
than
7/1/2014 despite the year is greater. How do I fix that? I did try to format as
%y/%m/%d

 but it does not fix that.


data$Date_Flag <- ifelse(data$COL2 > data$COL1, 0,1)


COL1       COL2
6/1/14     5/1/15
7/1/14     5/1/15


data$COL2<- as.Date(as.character(data$COL2, format="%y/%m/%d"))
data$COL1<- as.Date(as.character(data$COL1, format="%y/%m/%d"))


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Hi Mark,


Instead of 1 and 0. It generates NA

 NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA



________________________________
From: Mark Sharp <msharp at TxBiomed.org>
Sent: Wednesday, August 23, 2017 11:28:39 AM
To: Patrick Casimir
Cc: r-help at r-project.org
Subject: Re: [R] Comparing 2 dale columns

Patrick,

## Run the following script an notice the different values of the dataframe
"data" in each instance.

# I understand you have done something like the following:
data <- data.frame(COL1 = c("6/1/14", "7/1/14"),
                   COL2 = c("5/1/15", "5/1/15"),
stringsAsFactors = FALSE)
data$Date_Flag <- ifelse(data$COL2 > data$COL1, 0,1)
data
data$COL2 <- as.Date(as.character(data$COL2, format = "%y/%m/%d"))
data$COL1 <- as.Date(as.character(data$COL1, format = "%y/%m/%d"))
data$Date_Flag <- ifelse(data$COL2 > data$COL1, 0,1)
data

# What you may want instead is the following:
data <- data.frame(COL1 = c("6/1/14", "7/1/14"),
                   COL2 = c("5/1/15", "5/1/15"),
stringsAsFactors = FALSE)
data
## strptime() converts the character vector to POSIXct so you do not necessarily
## need the as.Date. However, they are not the same and you may need the Date
## class.
data$COL2 <- as.Date(strptime(data$COL2, format = "%m/%d/%y"))
data$COL1 <- as.Date(strptime(data$COL1, format = "%m/%d/%y"))
data
data$Date_Flag <- ifelse(data$COL2 > data$COL1, 0,1)
data


R. Mark Sharp, Ph.D.
msharp at TxBiomed.org




> On Aug 23, 2017, at 9:53 AM, Patrick Casimir <patrcasi at nova.edu>
wrote:
>
> data$Date_Flag <- ifelse(data$COL2 > data$COL1, 0,1)
>
>
> COL1       COL2
> 6/1/14     5/1/15
> 7/1/14     5/1/15
>
>
> data$COL2<- as.Date(as.character(data$COL2,
format="%y/%m/%d"))
> data$COL1<- as.Date(as.character(data$COL1,
format="%y/%m/%d"))
>
CONFIDENTIALITY NOTICE: This e-mail and any files and/or...{{dropped:13}}

Thanks. But when I apply your codes I get all NA instead of TRUE and FALSE

________________________________
From: PIKAL Petr <petr.pikal at precheza.cz>
Sent: Wednesday, August 23, 2017 11:20:00 AM
To: Patrick Casimir; r-help at r-project.org
Subject: RE: Comparing 2 dale columns

Hi

your code is wrong.

I get
> test<-read.table("clipboard", header=T)
> str(test)
'data.frame':   2 obs. of  2 variables:
 $ COL1: Factor w/ 2 levels "6/1/14","7/1/14": 1 2
 $ COL2: Factor w/ 1 level "5/1/15": 1 1
> test$COL2<- as.Date(as.character(test$COL2,
format="%y/%m/%d"))
> test$COL1<- as.Date(as.character(test$COL1,
format="%y/%m/%d"))
                                                                                
^^^^^^^^^^^^^^^^^^^^^^^
incorrect parentheses position, wrong y,m,d

Using correct syntax I get correct result.
> test$COL2<- as.Date(test$COL2, format="%d/%m/%y")
> test$COL1<- as.Date(test$COL1, format="%d/%m/%y")
>
> test$COL2 > test$COL1
[1] TRUE TRUE
> test
        COL1       COL2
1 2014-01-06 2015-01-05
2 2014-01-07 2015-01-05
>
Cheers
Petr
> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Patrick
> Casimir
> Sent: Wednesday, August 23, 2017 4:54 PM
> To: r-help at r-project.org
> Subject: [R] Comparing 2 dale columns
>
> Dear R fellows,
>
>
> I created a new column Date_flag to compare the dates of COL1 and COL2
> using the code below. But it showed that 5/1/15 is greater than 6/1/2014
and
> 5/1/2015 greater than
> 7/1/2014 despite the year is greater. How do I fix that? I did try to
format as
> %y/%m/%d
>
>  but it does not fix that.
>
>
> data$Date_Flag <- ifelse(data$COL2 > data$COL1, 0,1)
>
>
> COL1       COL2
> 6/1/14     5/1/15
> 7/1/14     5/1/15
>
>
> data$COL2<- as.Date(as.character(data$COL2,
format="%y/%m/%d"))
> data$COL1<- as.Date(as.character(data$COL1,
format="%y/%m/%d"))
>
>
>       [[alternative HTML version deleted]]
>
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