Smith, Phil
2006-Apr-17 20:05 UTC
[R] Function for computing the difference between 2 dates in months
Folks:
With the help of David L. Reiner, I've developed a function that
computes the number of months between 2 dates, x and y.
num.months <- function ( x , y )
{
x <- as.Date( x )
y <- as.Date( y )
seeq <- seq(from=x , to=y , by="months")
ans <- length( seeq ) - 1
if ( max( seeq) > y ) ans <- ans -1
ans
}
To ease your reading this function, I've left out some data cleaning
issues, and it is assumed that x <= y and that x and y were output from
as.date function (note the lower case "d" in as.date). The postscript
below provides 2 examples.
Anyone who wishes to comment or recommend a more accurate (or correct!)
method is welcome.
Best regards,
Phil Smith
Centers for Disease Control and Prevention
Example #1:
> x<-c( "2004-02-28" )
> y<-c( "2004-04-27" )
> num.months ( x , y )
[1] 1>
Example #2:
> x<-c( "2004-01-31" )
> y<-c( "2004-04-22" )
> num.months ( x , y )
[1] 2
Ana Patricia Martins
2006-Apr-19 13:44 UTC
[R] Function for computing the difference between 2 dates in months
Hi,
I tried to apply the function you developed to my data file, which had to be
created as follows:
date1<-sub(' - -
','',paste(substring(ie[,],257,260),substring(ie[,],255,256),substring(ie[,]
,253,254),sep="-"))
Your functions works well only in example #1 but when I applied a
"cycle"
(if clause) doesn't work (example #2 and #3).
Example #1:
a35641<-num.months (dados$date1[35641],dados$date2[35641])
[1] 68
Example #2:
mes1<-with(dados,ifelse(date1!=" - -
",num.months(date1,date2),""))>Error in fromchar(x) : character string is not in a standard unambiguous
format
Example #3:
mes<-c(rep("NA",length(dados$date1)))
for (i in 1:m){
if (dados$date1[i]!=" - - ")
mes[i]<-num.months(dados$date1[i],dados$date2[i])}
Do you think you can solve this problem?
Thanks in advance for your cooperation.
Best regards,
Ana Patricia Martins
-------------------------------------------
Servi?o M?todos Estat?sticos
Departamento de Metodologia Estat?stica
INE - Portugal
Telef: 218 426 100 - Ext: 3210
E-mail: ana.pmartins at ine.pt
-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Smith, Phil
Sent: segunda-feira, 17 de Abril de 2006 21:06
To: r-help at stat.math.ethz.ch
Subject: [R] Function for computing the difference between 2 dates in months
Folks:
With the help of David L. Reiner, I've developed a function that
computes the number of months between 2 dates, x and y.
num.months <- function ( x , y )
{
x <- as.Date( x )
y <- as.Date( y )
seeq <- seq(from=x , to=y , by="months")
ans <- length( seeq ) - 1
if ( max( seeq) > y ) ans <- ans -1
ans
}
To ease your reading this function, I've left out some data cleaning
issues, and it is assumed that x <= y and that x and y were output from
as.date function (note the lower case "d" in as.date). The postscript
below provides 2 examples.
Anyone who wishes to comment or recommend a more accurate (or correct!)
method is welcome.
Best regards,
Phil Smith
Centers for Disease Control and Prevention
Example #1:
> x<-c( "2004-02-28" )
> y<-c( "2004-04-27" )
> num.months ( x , y )
[1] 1>
Example #2:
> x<-c( "2004-01-31" )
> y<-c( "2004-04-22" )
> num.months ( x , y )
[1] 2
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