Created
September 10, 2010 17:40
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# per http://stackoverflow.com/questions/3684484/peak-detection-in-a-2d-array | |
require 'pp' | |
NUM_PEAKS = 5 | |
NEIGHBOR_DISTANCE = 1 | |
data = [[1,2,3,4,5], | |
[2,6,4,4,6], | |
[3,6,7,4,3], | |
] | |
def tuples(matrix) | |
tuples = [] | |
matrix.each_with_index { |row, ri| | |
row.each_with_index { |value, ci| | |
tuples << [value, ri, ci] | |
} | |
} | |
tuples | |
end | |
def neighbor?(t1, t2, distance = 1) | |
[1,2].each { |axis| | |
return false if (t1[axis] - t2[axis]).abs > distance | |
} | |
true | |
end | |
# convert the matrix into a sorted list of tuples (value, row, col), highest peaks first | |
sorted = tuples(data).sort_by { |tuple| tuple.first }.reverse | |
# the list of peaks that don't have neighbors | |
non_neighboring_peaks = [] | |
sorted.each { |candidate| | |
# always take the highest peak | |
if non_neighboring_peaks.empty? | |
non_neighboring_peaks << candidate | |
puts "took the first peak: #{candidate}" | |
else | |
# check that this candidate doesn't have any accepted neighbors | |
is_ok = true | |
non_neighboring_peaks.each { |accepted| | |
if neighbor?(candidate, accepted, NEIGHBOR_DISTANCE) | |
is_ok = false | |
break | |
end | |
} | |
if is_ok | |
non_neighboring_peaks << candidate | |
puts "took #{candidate}" | |
else | |
puts "denied #{candidate}" | |
end | |
end | |
} | |
pp non_neighboring_peaks |
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