CODEWITHSUNDEEP
rstatistics
Evan Scott
Evan Scott

Reputation: 11

Returning value from column if value in separate column meets certain parameters

I want to be able to search or filter a column and if it meets certain parameters, return the value in another column (but at a different point).

So for example,
L <- matrix(rnorm(500, mean=50, sd=4), nrow=100, ncol=5, byrow=FALSE)
L <-as.data.frame(L)
colnames(L)<-c("1","2","3","4","5")

If L[,"1"] >= 58 I want to print the value of the value in L[,"4"] that is 5 rows lower.

So if L[1,1] had a value of 60, I want the value of L[6,4] and do this for all values in L[,"1"] that meet these parameters. Preferably with a printout that gives a clear indication of multiple pairing values (ie the corresponding coordinates).

Help starting this would be greatly appreciated and obviously solutions are helpful as well. I know how to filter and make a subset of a data frame consisting of certain values, but I have no idea how to pull objects at a different portion like in this problem.

Upvotes: 0

Views: 463

Answers (1)

Edward
Edward

Reputation: 5537

Well, as for help getting started, the which function will be helpful. It returns the indices that meet a certain criteria - so to see all rows for which column "1" is greater than 58, you can use:

matched.indices <- which(L[,"1"] > 58)

To then find all the indices that are 5 rows lower, we can simply add 5:

shifted.indices <- matched.indices + 5

From here, you can print out the pairs of values and coordinates however you want to. One way would be as follows:

len <- length(matched.indices)    
cat(paste(rep("[",len), matched.indices, rep(",1],", len),     # 1st coordinate
        rep("[",len), shifted.indices, rep(",4] = ", len),     # 2nd coordinate
        L[matched.indices, "1"],                               # 1st value
        rep(",", len),
        L[shifted.indices, "4"],                               # 2nd value
        sep=""),sep="\n")

The output will look like this:

[4,1],[9,4] = 58.9223792285318,48.5241852967192
[70,1],[75,4] = 58.5015984791419,55.3071097158975
[76,1],[81,4] = 61.7996739529131,51.6725968541657
[85,1],[90,4] = 58.0881601753751,40.2410431328713
[92,1],[97,4] = 58.1622310810397,50.6118549434608
[96,1],[101,4] = 58.4433975051732,NA

As I said, it's just a start. Specifically, you did not mention what to do with the last 5 rows; my solution will just print NA for those values (as with the last row above). If you want to clarify that point, I'll update the answer accordingly.

Upvotes: 1

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