ENH: add compression to pulseq output

src/sequence_io/pulseq_io/parsers/shapes.jl

 struct CompressedPulseqShape
     num :: Int
-    samples :: Vector{Float64}
+    samples :: Vector{Number}
 end
 
 
@@ -57,14 +57,47 @@ function uncompress(compressed::CompressedPulseqShape)
     return PulseqShape(amplitudes)
 end
 
+function compress(shape::PulseqShape)
+    amplitudes = shape.samples
+    derivative = amplitudes[2:end] - amplitudes[1:end-1]
+
+    current_value = amplitudes[1]
+    compressed = Number[amplitudes[1]]
+
+    nrepeats = -1
+    for sample in derivative
+        if sample ≈ current_value
+            nrepeats += 1
+            if iszero(nrepeats)
+                push!(compressed, current_value)
+            end
+        else
+            if nrepeats != -1
+                push!(compressed, nrepeats)
+                nrepeats = -1
+            end
+            current_value = sample
+            push!(compressed, current_value)
+        end
+    end
+    if nrepeats >= 0
+        push!(compressed, nrepeats)
+    end
+    if length(compressed) >= length(amplitudes)
+        return CompressedPulseqShape(length(amplitudes), amplitudes)
+    else
+        return CompressedPulseqShape(length(amplitudes), compressed)
+    end
+end
+
 function gen_section(comp:: PulseqComponents, ::Val{:shapes})
     res = PulseqSection{:shapes}(String[])
     for index in sort([keys(comp.shapes)...])
-        shape = comp.shapes[index]
+        shape = compress(comp.shapes[index])
         append!(res.content, [
             "",
             "shape_id $index",
-            "num_samples $(length(shape.samples))"
+            "num_samples $(shape.num)"
         ])
         for sample in shape.samples
             push!(res.content, string(sample))

test/test_IO.jl

@@ -128,4 +128,20 @@
             end
         end
     end
+    @testset "Test Pulseq shape compression" begin
+        import MRIBuilder.SequenceIO.PulseqIO.Parsers: compress, uncompress
+        import MRIBuilder.SequenceIO.PulseqIO.Types: PulseqShape
+
+        for (amplitudes, result) in [
+            ([0., 0.1, 0.25, 0.5, ones(7)..., 0.75, 0.5, 0.25, 0.], [0., 0.1, 0.15, 0.25, 0.5, 0., 0., 4, -0.25, -0.25, 2]),
+            (zeros(100), [0., 0., 98]),
+            (ones(100), [1., 0., 0., 97]),
+        ]
+            shape = PulseqShape(amplitudes)
+            res = compress(shape)
+            @test res.num == length(amplitudes)
+            @test all(res.samples == result)
+            @test all(uncompress(res).samples == amplitudes)
+        end
+    end
 end
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