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I have a vector with random numbers from 1-7 and I want to be able to determine the next number in the vector that follows the first value so that I can look for patterns and get a 7x7 matrix of values that shows how often a specific number follows another.

First number in rows and count of next number in columns.

I am trying to do this with a double loop currently, but am getting confused in the process.

For example-

Example vector-

floor(runif(10,1,8))
[1] 3 5 6 6 6 1 7 7 5 3

Answer-

  1  2  3  4  5  6  7
1 0  0  0  0  0  0  1
2 NA NA NA NA NA NA NA
3 0  0  0  0  1  0  0
4 NA NA NA NA NA NA NA
5 0  0  1  0  0  1  0
6 1  0  0  0  0  3  0
7 0  0  0  0  1  0  1
AtmoSci
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1 Answers1

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Given a vector

v <- c(3, 5, 6, 6, 6, 1, 7, 7, 5, 3)

if you call table() on the vector you get a count of each element

table( v )
# v
# 1 3 5 6 7 
# 1 2 2 3 2

If you call table() on mulitple vectors, you get a count for each combination of values.

Since you want to 'count' the number of times a value appears with the value next to it, you can call table() on the original vector, and the same vector shifted one-value to the right. 

table( v[1:(length(v)-1)], v[2:length(v)] )

#  y
# x  1 3 5 6 7
#  1 0 0 0 0 1
#  3 0 0 1 0 0
#  5 0 1 0 1 0
#  6 1 0 0 2 0
#  7 0 0 1 0 1

Which can be made more succinct (courtesy of Julius Vainora ) by

table(head(v, -1), tail(v, -1))

Note: the result doesn't include the NA rows you've got in your question.

SymbolixAU
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