CODEWITHSUNDEEP
r
Deset
Deset

Reputation: 947

Use Twofold which() condition but keep Indices from the beginning in R

I have the following data:

eData<- c(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,-2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
                  ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0
                  ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,-2,0,2,0,-2,2,-2,2,0,0,-2,0,2,0,-2,0,0,2,-2,0,1,0,1
                  ,0,-2,2,-2,0,1,0,1,0,-2,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,1,0,-2,2,-2,0,1,0,0,1,0,-2,0,2,0,-2,0,2,0,0
                  ,0,-2,0,2,-2,0,2,0,-2,1,1,0,-2,0,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
                  ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
                  ,0,0,0,0,0,0,0,0,0,-2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
                  ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,-2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
                  ,0,0,0,0,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,-2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
                  ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
                  ,0,0,0,0,-2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
                  ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)

In a next step i search for all Indices which have the value -2 but I want the value next to it so my code is:

which(eData == -2) + 1
[1]  25 114 118 120 124 128 132 138 140 146 164 166 173 177 183 186 190 194 281 343 387 456

Looking at the actual data I want all values > 0:

eData[which(eData == -2) + 1]
[1] 0 0 2 2 0 0 0 2 0 0 2 0 0 0 0 0 1 0 0 0 0 0

So i do:

which( eData[which(eData == -2) + 1] > 0)
3  4  8 11 17

But the final result I really want is:

result
118 120 138 164 190

Meaning the corresponding Indices for the original data. So that i can do:

eData[result]
2 2 2 2 1

like 

eData[118] 
2
etc.

How can I archive something like this all I tried yielded just an error message or got me just the "wrong" result 3 4 8 11 17:

which( eData[which(eData == -2) + 1] > 0)

But I want the Original values. I have the impression that it cant be that difficult, but cant figure it out myself.

Upvotes: 0

Views: 73

Answers (1)

etienne
etienne

Reputation: 3678

From what you are saying, you are looking for strictly positive values which are after a value equal to -2. You can do an intersect in order to have the position of those numbers.

intersect(which(eData >0),which(eData == -2)+1)
# [1] 118 120 138 164 190

and you indeed have

eData[intersect(which(eData >0),which(eData == -2)+1)]
# [1] 2 2 2 2 1 # the values of eData(118), ... : all > 0

eData[intersect(which(eData >0),which(eData == -2)+1)-1]
# [1] -2 -2 -2 -2 -2 # the values of eData(118-1), ... : all equal to -2

or you could also use

which(eData>0 & c(NA,eData[-length(eData)])==-2)
# [1] 118 120 138 164 190

Upvotes: 2

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