R subtracting vectors - numeric 0 answer

Question

I try to subtract two vectors with each length 7 from another. Yet my results won't produce another vector, I simply get numeric 0 and data 0. Any idea?

#You will buy these stocks on rows/days 7, 8, 9, 15, 26, 33 and 53. (1 day after days apple dropped more than 2% )
#Assign the prices of the stocks on these days to a vector
SLB_buy = c(SLB_close[7],SLB_close[8],SLB_close[9],SLB_close[15],SLB_close[26],SLB_close[34],SLB_close[53])
SLB_buy
           SLB.Close
2015-08-21     77.50
2015-08-24     73.87
2015-08-25     72.52
2015-09-02     75.41
2015-09-18     72.54
2015-09-30     68.97
2015-10-27     76.95

#You will sell these stocks on rows/days 10, 11, 12, 18, 29, 36 and 56. (3 day after purchase)
#Assign the prices of the stocks on these days to a vector
SLB_sell =c(SLB_close[10],SLB_close[11],SLB_close[12],SLB_close[18],SLB_close[29],SLB_close[36],SLB_close[56])
SLB_sell
       SLB.Close
2015-08-26     70.09
2015-08-27     73.85
2015-08-28     76.06
2015-09-08     75.54
2015-09-23     71.94
2015-10-02     70.32
2015-10-30     78.16

#Your profit is equal to the sales price - buy price. Hence substract the previous vectors from each other.
SLB_sell - SLB_buy
Data:
numeric(0)

Index:
numeric(0)

Answer 1

I have copied your vectors from clipboard. What I did to achieve what you want:

# remove SLB.Close, which is the first element of the vector. 
#It might not be the case for your actual vector though.
SLB_buy<-SLB_buy[-1]
# remove the dates and transform in numeric

SLB_buy<-substring(SLB_buy, 11)
SLB_buy<-as.numeric(SLB_buy) 

# depending on your actual vector the position to start substring 
#(in this case 11) might vary.

Do the same with the second vector and subtract

SLB_sell-SLB_buy