I´m quite new at programming, and I started with R. I wanted to make a script which takes as input a matrix with the columns: time, x, y (coordenates) and then divide the time spent in each quadrant of a circular area. I have a roughly done script, but for any reason I don´t understand, when I execute the for loop in the editor, it appears all the letters red in the console with a "+" at the beginning of each line, which doesn´t let me open any other object any more when I call it.

```
set.seed(20)
x = matrix(rnorm(10,3,4),10,1)
y = matrix (rnorm(10,3,4),10,1)
time = matrix (1:10,10,1)
a = cbind (time,x,y)
colnames(a) = c("time","x","y")
upperright = a[,2] > 0 && a[,3] > 0
upperleft = a[,2] < 0 && a[,3] > 0
lowerright = a[,2] > 0 && a[,3] < 0
lowerleft = a[,2] < 0 && a[,3] < 0
calculation <- function () {
upperrightquadrant = 0
upperleftquadrant = 0
lowerrightquadrant = 0
lowerleftquadrant = 0
for (i in c(1:nrow(a))){
if (upperright) upperrightquadrant <<- sum((a[i,1]-a[i-1,1]))
if (upperleft)upperleftquadrant <<- sum((a[i,1]-a[i-1,1]))
if (lowerright) lowerrightquadrant <<-sum((a[i,1]-a[i-1,1]))
if (lowerleft) lowerleftquadrant <<- sum((a[i,1]-a[i-1,1]))
}}
output = lapply (a, calculation)
```

### Answer1:

The `+`

symbols are only a way to show that the current statement is conitnuation of the previous lines's statement. That's perfectly OK. There are a couple of other problems with your program which are stopping it from producing your intended result. If I have in fact, understood what you are trying to do, I have added a possible solution at the end. First, let me suggest the edits and the reason for them:

`&`

should have been used instead of `&&`

. `&`

is the vectorized operator. So, `upperright = a[,2] > 0 & a[,3] > 0`

instead of `upperright = a[,2] > 0 && a[,3] > 0`

.</li>
<li>You are passing a value to the function so its definition should include the parameter `calculation <- function (a)`

instead of `calculation <- function ()`

.</li>
<li>upperright, upperleft, ... are vectors and you should check individual elements instead of the whole vector `if (upperright[i])`

instead of `if (upperright)`

.</li>
<li>Problem with `sum((a[i,1]-a[i-1,1]))`

at i==1, i-1 equals 0. If you are only counting, incrementing the count by 1 should be sufficient.</li>
<li>The objects upperrightquadrant, upperleftquadrant, ... are in your function environment only. So, no need for `<<-`

.</li>
<li>Finally, as you have already written the `for`

loop to iterate over your matrix rowwise, no need for lapply or other similar looping functions.

Only a suggestion: Use `<-`

operator for assignments instead of `=`

.

Now, the corrected program:

```
set.seed(20)
x = matrix(rnorm(10,3,4),10,1)
y = matrix (rnorm(10,3,4),10,1)
time = matrix (1:10,10,1)
a = cbind (time,x,y)
colnames(a) = c("time","x","y")
upperright = a[,2] > 0 & a[,3] > 0
upperleft = a[,2] < 0 & a[,3] > 0
lowerright = a[,2] > 0 & a[,3] < 0
lowerleft = a[,2] < 0 & a[,3] < 0
calculation <- function (a) {
upperrightquadrant = 0
upperleftquadrant = 0
lowerrightquadrant = 0
lowerleftquadrant = 0
for (i in c(1:nrow(a))){
if (upperright[i]) upperrightquadrant <- upperrightquadrant + 1
if (upperleft[i]) upperleftquadrant <- upperleftquadrant + 1
if (lowerright[i]) lowerrightquadrant <- lowerrightquadrant + 1
if (lowerleft[i]) lowerleftquadrant <- lowerleftquadrant + 1
}
list(upperrightquadrant = upperrightquadrant, upperleftquadrant = upperleftquadrant,
lowerrightquadrant = lowerrightquadrant, lowerleftquadrant = lowerleftquadrant)
}
output = calculation(a)
print(a) # input
print(output) # output
```

### EDIT

This is the edit for what you requested (Case where time instances are not contiguous). Just replace the `for`

loop with this one:

```
for (i in c(1:nrow(a))){
if(i>1){
if (upperright[i]) upperrightquadrant <- upperrightquadrant + a[i, 1] - a[i-1, 1]
if (upperleft[i]) upperleftquadrant <- upperleftquadrant + a[i, 1] - a[i-1, 1]
if (lowerright[i]) lowerrightquadrant <- lowerrightquadrant + a[i, 1] - a[i-1, 1]
if (lowerleft[i]) lowerleftquadrant <- lowerleftquadrant + a[i, 1] - a[i-1, 1]
} else {
if (upperright[i]) upperrightquadrant <- upperrightquadrant + a[i, 1]
if (upperleft[i]) upperleftquadrant <- upperleftquadrant + a[i, 1]
if (lowerright[i]) lowerrightquadrant <- lowerrightquadrant + a[i, 1]
if (lowerleft[i]) lowerleftquadrant <- lowerleftquadrant + a[i, 1]
}
}
```

Hope, this helps.