I am trying to implement following algorithm in R:
Iterate(Cell: top)
While (top != null)
Print top.Value
top = top.Next
End While
End Iterate
Basically, given a list, the algorithm should break as soon as it hits 'null' even when the list is not over.
myls<-list('africa','america south','asia','antarctica','australasia',NULL,'europe','america north')
I had to add a for loop for using is.null() function, but following code is disaster and I need your help to fix it.
Cell <- function(top) {
#This algorithm examines every cell in the linked list, so if the list contains N cells,
#it has run time O(N).
for (i in 1:length(top)){
while(is.null(top[[i]]) !=TRUE){
print(top)
top = next(top)
}
}
}
You may run this function using:
Cell(myls)
You were close but there is no need to use for(...) in this
construction.
Cell <- function(top){
i = 1
while(i <= length(top) && !is.null(top[[i]])){
print(top[[i]])
i = i + 1
}
}
As you see I've added one extra condition to the while loop: i <= length(top) this is to make sure you don't go beyond the length of the
list in case there no null items.
However you can use a for loop with this construction:
Cell <- function(top){
for(i in 1:length(top)){
if(is.null(top[[i]])) break
print(top[[i]])
}
}
Alternatively you can use this code without a for/while construction:
myls[1:(which(sapply(myls, is.null))[1]-1)]
Check this out: It runs one by one for all the values in myls and prints them but If it encounters NULL value it breaks.
for (val in myls) {
if (is.null(val)){
break
}
print(val)
}
Let me know in case of any query.
Related
Greetings I am getting an error of
Error in if (nrow(pair) == 0) { :argument is of length zero
I have checked the other answers but do not seem to work on a variable like mine. Please check code below, please assist if you can.
pair<-NULL
if(exists("p.doa.ym")) pair <- rbind(pair, p.doa.ym[,1:2])
if(exists("p.doa.yd")) pair <- rbind(pair, p.doa.yd[,1:2])
if(nrow(pair) == 0) {
print("THERE ARE NO MATCHES FOR TODAY. STOP HERE")
quit()
}
Since you set pair=NULL and then it might happen that pair stays null if those two if statements are not true, you either need to check if pair is null first, or you could set pair to an empty data frame, or something else.
One option:
if (!is.null(pair)) {
if (nrow(pair)==0) {
# your code
}
}
Another option:
pair=data.frame()
# your code
I am trying to change a variable in a function but even tho the function is producing the right values, when I go to use them in the next sections, R is still using the initial values.
I created a function to update my variables NetN and NetC:
Reproduction=function(NetN,NetC,cnrep=20){
if(NetC/NetN<=cnrep) {
DeltaC=NetC*p;
DeltaN=DeltaC/cnrep;
Crep=Crep+DeltaC;
Nrep=Nrep+DeltaN;
Brep=(Nrep*14+Crep*12)*2/1e6;
NetN=NetN-DeltaN; #/* Update N, C values */
NetC=NetC*(1-p)
print ("'Using C to allocate'")
}
else {
print("Using N to allocate");
DeltaN=NetN*p;
DeltaC=DeltaN*cnrep;
Nrep=Nrep+DeltaN;
Crep=Crep+DeltaC;
Brep=(Nrep*14+Crep*12)*2/1e6;
NetN=NetN*(1-p);
NetC=NetC-DeltaC;
} } return(c(NetC=NetC,NetN=NetN,NewB=NewB,Crep=Crep,Nrep=Nrep,Brep=Brep))}
When I use my function by say doing:
Reproduction(NetN=1.07149,NetC=0.0922349,cnrep=20)
I get the desired result printed out which includes:
NetC=7.378792e-02
However, when I go to use NetC in the next section of my code, R is still using NetC=0.0922349.
Can I make R update NetC without having to define a new variable?
In R, in general, functions shouldn't change things outside of the function. It's possible to do so using <<- or assign(), but this generally makes your function inflexible and very surprising.
Instead, functions should return values (which yours does nicely), and if you want to keep those values, you explicitly use <- or = to assign them to objects outside of the function. They way your function is built now, you can do that like this:
updates = Reproduction(NetN = 1.07149, NetC = 0.0922349, cnrep = 20)
NetC = updates["NetC"]
This way, you (a) still have all the other results of the function stored in updates, (b) if you wanted to run Reproduction() with a different set of inputs and compare the results, you can do that. (If NetC updated automatically, you could never see two different values), (c) You can potentially change variable names and still use the same function, (d) You can run the function to experiment/see what happens without saving/updating the values.
If you generally want to keep NetN, NetC, and cnrep in sync, I would recommend keeping them together in a named vector or list, and rewriting your function to take that list as input and return that list as output. Something like this:
params = list(NetN = 1.07149, NetC = 0.0922349, cnrep = 20)
Reproduction=function(param_list){
NetN = param_list$NetN
NetC = param_list$NetC
cnrep = param_list$cnrep
if(NetC/NetN <= cnrep) {
DeltaC=NetC*p;
DeltaN=DeltaC/cnrep;
Crep=Crep+DeltaC;
Nrep=Nrep+DeltaN;
Brep=(Nrep*14+Crep*12)*2/1e6;
NetN=NetN-DeltaN; #/* Update N, C values */
NetC=NetC*(1-p)
print ("'Using C to allocate'")
}
else {
print("Using N to allocate");
DeltaN=NetN*p;
DeltaC=DeltaN*cnrep;
Nrep=Nrep+DeltaN;
Crep=Crep+DeltaC;
Brep=(Nrep*14+Crep*12)*2/1e6;
NetN=NetN*(1-p);
NetC=NetC-DeltaC;
}
## Removed extra } and ) ??
return(list(NetC=NetC, NetN=NetN, NewB=NewB, Crep=Crep, Nrep=Nrep, Brep=Brep))
}
This way, you can use the single line params <- Reproduction(params) to update everything in your list. You can access individual items in the list with either params$Netc or params[["NetC"]].
You can suggest me any sort of answers, not necessarily need using conditional statements and Loops.
I have the data set with several ids and and three alert or groups.
here is the image for the concept:
and here is the actual Data set for one ID: Click me
Concept is:
I have three alert: Relearn - Rebuild - Replace.
and after relearn: rebuild or replace can come but relearn cannot come
and after rebuild: replace can come but relearn cannot come
after replace: relearn and rebuild cannot come. if there is any replace only that can come
I have attached the image and Dataset for better clear understanding and Here is my try:
temp1 = NULL
temp2 = NULL
sql50 = NULL
for(i in 1:nrow(BrokenPins)) #First Loop
{
sql50 = sqldf(paste("select * from rule_data where key = '",BrokenPins[i,1],"'",sep = ""))
for(j in 1:nrow(sql50))
{ #Second Loop
while (head(sql50$Flag,1) == sql50$Flag[j] )
{
temp1 = sql50[j,]
temp2 = rbind(temp2,temp1)
print("Send")
if(j == 1 || sql50$Flag[j] == sql50$Flag[j-1])
{
j = j+1
}
else(sql50$Flag[j] > sql50$Flag[j-1])
{
break
}
}
}
}
First loop will go through each id and second loop will give me all the alert for that id.
so in the image i have added send and dont send. it wont be in actual table. that basically means send means copy it to new dataframe like i am doing above rbind in the code and dont send means dont copy it. This Above piece of code will run but only take the first and end it.
Finally, Based On above Data set Click me: that is for one ID (key), Flag (1 - Relearn, 2-Rebuild,3-replace). so based on this dataset. my output should have Row 1, 2 and 7 because First Relearn[Flag 1] came then Rebuild[Flag 2] then again relearn[Flag 1]cannot come, only rebuild [Flag 2] and replace[Flag 2] can.
can you help me solve this concept?
One thing I notice is that you use else and also provided a condition; you should only use else when you want every case that is not included in the condition of your if statement. Basically, instead of using else(sql50$Flag[j] > sql50$Flag[j-1]) you should be using else if(sql50$Flag[j] > sql50$Flag[j-1]).
HI i just started learning R and finding this problem to be really interesting where I just run a code directly without wrapping in a function it works but when I place it inside a function it doesn't work, What can be possible reason?
fill_column<-function(colName){
count <- 0
for(i in fg_data$particulars) {
count <- count +1
if(grepl(colName, i) && fg_data$value[count] > 0.0){
fg_data[,colName][count] <- as.numeric(fg_data$value[count])
} else {
fg_data[,colName][count] <- 'NA'
}
}
}
fill_column('volume')
Where I am creating new column named volume it this string exists in particulars column.
I have added a comment where solution given by another question does not work for me, Please look at my comment below.
Finally I got it working but reading another answer on SO, here is the solution:
fill_column <- function(colName){
count <- 0
for(i in fg_data$particulars) {
count <- count +1
if(grepl(colName, i) && fg_data$value[count] > 0.0){
fg_data[,colName][count] <- as.numeric(fg_data$value[count])
} else {
fg_data[,colName][count] <- 'NA'
}
}
return(fg_data)
}
fg_data = fill_column('volume')
Now reason, Usually in any language when we modify global object inside any function it reflects on global object immediately but in R we have to return the modified object from function and then assign it again to global object to see our changes. or another way for doing this is to assign local object from within the function to global context using envir=.GlobalEnv.
I am trying to write a function that reads a vector of numbers element wise and then storing them into a container. This is meant as a practice before I code something with if conditions.
My approach has failed so far, as the function returns a null statement, instead of what I wanted. I tried writing it in script form and it it worked, but somehow it malfunctioned when written as a function.
Here's the code I used.
amieven<-function(x){
flag<-numeric()
for(i in 1:length(x)){
flag[i]=x[i]
}
}
The script version that worked fine looks like this:
flag<-numeric()
for (i in 1:length(x))
flag[i]=x[i]
Assuming your goal is to return the container called flag, then you simply need to specify flag as the return value.
amieven<-function(x){
flag<-numeric()
for(i in 1:length(x)){
flag[i]=x[i]
}
return(flag)
}
or simply
amieven<-function(x){
flag<-numeric()
for(i in 1:length(x)){
flag[i]=x[i]
}
flag
}