Alan -
ALAN SMITH wrote:
Hello R users and developers,
I am trying to write several functions (fairly new at this) in order
to avoid using loops on large data frames (because they are slow). I
wrote the function below and it seems to get hung on the first part of
the if statement and then applies that condition to rest of the
function. So if (x-y) is greater than 0 the function uses the true
statement for the calculations. Could someone please offer some
advise on how to write these functions a little better or a type
"apply" that I may use with two (or more) different vectors of data
required by a single functions.
####################### Examples
#######################################################
## example 1 ###
x<-c(5,6,4,3,5,3,1)
y<-c(1,6,2,1,7,1,9)
folds<-function(x,y) (if((x-y)>=0) {2^(x-y)} else{-(2^abs(x-y))})
z<-folds(x,y)
check<-cbind(x,y,z)
View(check)
Warning message:
In if ((x - y) >= 0) { :
the condition has length > 1 and only the first element will be used
### why will it only use the first element and how to I get around
this ####
When learning R, you have the power of the interpreter at all times.
You have defined x and y above to be numeric vectors of length 7 each.
Try typign x - y at the interpreter, and you'll see you get another
numeric vector of length 7. Now try (x - y) >= 0 , and you'll get a
logical vector of length 7. However, if does not want a logical vector
of length 7, it wants a logical vector of length 1, see the 'cond'
argument of ?if. However, the ifelse function should do what you want,
see ?ifelse.
Here's an example using it
folds2 <- function(x, y) {
ifelse(x - y >= 0, 2^(x - y), -(2^abs(x - y)))
}
folds2(x, y) should give you your answer...
## example 2 making the fist comparison negative ###
x1<-c(5,6,4,3,5,3,1)
y1<-c(11,6,2,1,7,1,9)
folds<-function(x,y) (if((x-y)>=0) {2^(x-y)} else{-(2^abs(x-y))})
z1<-folds(x1,y1)
check2<-cbind(x1,y1,z1)
View(check2)
Warning message:
In if ((x - y) >= 0) { :
the condition has length > 1 and only the first element will be used
Same idea as above here...
################################################################################
#### loop I am trying to avoid writing many many times #####
folds2<-NULL
xy<-as.data.frame(cbind(x,y))
for (i in 1:nrow(xy)) {
diff<-xy$x[i]-xy$y[i]
folds2[i]<-if(diff>=0) {2^diff} else{-(2^abs(diff))}
}
xyz<-cbind(xy,folds2)
View(xyz)
#################
I'm not exactly sure what you'd like here, but hopefully with the above
you can figure it out. Let me know if you have any questions!
Best,
Erik Iverson
Thank you,
Alan
P.S. why does ?function not work
What do you expect it to do? It shows the help page for 'function' here.
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and provide commented, minimal, self-contained, reproducible code.
