[R] Using functions to change values in a data.frame

[Mark Knecht]

I'm having trouble with something that looks easy. (And I'm sure it
will be easier within about 1 minute of receiving my first response.)
Thanks in advance.

I have a collection of data frames that I need to add columns, do some
calculations and then fill in the new columns. Since I have a large
number of similar data frames I want to do this with functions to make
the code more readable and ensure that every frame is done the same
way. However my simple example doesn't work as I expected it to:

Here the R example code to cut and paste. The basic idea is to copy
positive values of y into p and negative values into l.

<START COPY>

AddCols = function (MyFrame) {
	MyFrame$p<-0
	MyFrame$l<-0
	return(MyFrame)
}

BinPosNeg = function (MyFrame) {
	ifelse(MyFrame$y>0,  MyFrame$p<-MyFrame$y,  MyFrame$l<MyFrame$y)
	return(MyFrame)
}

F1 <- data.frame(x=1:10, y=-4:5)
F1
F1 <- AddCols(F1)
F1
F1 <- BinPosNeg(F1)
F1

<END COPY>

My results below are weird. After the last function call F1 acts like
BinPosNeg always evaluated MyFrame$y>0. All updates went into p - none
into l.

What am I doing wrong?

Thanks,
Mark


MY RESULTS:

> AddCols = function (MyFrame) {
+ MyFrame$p<-0
+ MyFrame$l<-0
+ return(MyFrame)
+ }
>
> BinPosNeg = function (MyFrame) {
+ ifelse(MyFrame$y>0,  MyFrame$p<-MyFrame$y,  MyFrame$l<MyFrame$y)
+ return(MyFrame)
+ }
>
> F1 <- data.frame(x=1:10, y=-4:5)
> F1
    x  y
1   1 -4
2   2 -3
3   3 -2
4   4 -1
5   5  0
6   6  1
7   7  2
8   8  3
9   9  4
10 10  5
> F1 <- AddCols(F1)
> F1
    x  y p l
1   1 -4 0 0
2   2 -3 0 0
3   3 -2 0 0
4   4 -1 0 0
5   5  0 0 0
6   6  1 0 0
7   7  2 0 0
8   8  3 0 0
9   9  4 0 0
10 10  5 0 0
> F1 <- BinPosNeg(F1)
> F1
    x  y  p l
1   1 -4 -4 0
2   2 -3 -3 0
3   3 -2 -2 0
4   4 -1 -1 0
5   5  0  0 0
6   6  1  1 0
7   7  2  2 0
8   8  3  3 0
9   9  4  4 0
10 10  5  5 0
>