Hello,
Try the following.
dat <- read.table(text="
PT_ID IDX_DT OBS_DATE DAYS_DIFF OBS_VALUE CATEGORY
13 4549 2002-08-21 2002-08-20 -1 183 2
14 4549 2002-08-21 2002-11-14 85 91 1
15 4549 2002-08-21 2003-02-18 181 89 1
16 4549 2002-08-21 2003-05-15 267 109 2
17 4549 2002-08-21 2003-12-16 482 96 1
128 4839 2006-11-28 2006-11-28 0 179 2
", header=TRUE)
spl <- split(dat, dat$PT_ID)
idx <- sapply(spl, function(x) which.min(x$DAYS_DIFF))
res <- lapply(names(idx), function(nm) spl[[ nm ]][ idx[nm], ])
do.call(rbind, res)
And assign the return value of do.call to your result (reuse 'res').
Hope this helps,
Rui Barradas
Em 01-09-2012 18:10, WANG WEIJIA escreveu:
Hi,
I have encountered an issue about finding a date closest to another date
So this is how the data frame looks like:
PT_ID IDX_DT OBS_DATE DAYS_DIFF OBS_VALUE CATEGORY
13 4549 2002-08-21 2002-08-20 -1 183 2
14 4549 2002-08-21 2002-11-14 85 91 1
15 4549 2002-08-21 2003-02-18 181 89 1
16 4549 2002-08-21 2003-05-15 267 109 2
17 4549 2002-08-21 2003-12-16 482 96 1
128 4839 2006-11-28 2006-11-28 0 179 2
I need to find, the single observation, which has the closest date of
'OBS_DATE' to 'IDX_DT'.
For example, for 'PT_ID' of 4549, I need row 13, of which the OBS_DATE is just
one day away from IDX_DT.
I was thinking about using abs(), and I got this:
baseline<- function(x){
+
+ #remove all uncessary variables
+ baseline<- x[,c("PT_ID","DAYS_DIFF")]
+
+ #get a list of every unique ID
+ uniqueID <- unique(baseline$PT_ID)
+
+ #make a vector that will contain the smallest DAYS_DIFF
+ first <- rep(-99,length(uniqueID))
+
+ i = 1
+ #loop through each unique ID
+ for (PT_ID in uniqueID){
+
+ #for each iteration get the smallest DAYS_DIFF for that ID
+ first[i] <-
min(baseline[which(baseline$PT_ID==PT_ID),abs(baseline$DAYS_DIFF)])
+
+ #up the iteration counter
+ i = i + 1
+
+ }
+ #make a data frame with the lowest DAYS_DIFF and ID
+ newdata <- data.frame(uniqueID,first)
+ names(newdata) <- c("PT_ID","DAYS_DIFF")
+
+ #return the data frame containing the lowest GPI for each ID
+ return(newdata)
+ }
ldl.b<-baseline(ldl) #get all baseline ldl patient ID, total 11368 obs, all
unique#
Error in `[.data.frame`(baseline, which(baseline$PT_ID == PT_ID),
abs(baseline$DAYS_DIFF)) :
undefined columns selected
Can anyone help me in figuring out how to get the minimum value of the absolute value of DAYS_DIFF for unique ID?
Thanks a lot
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