You might be looking for something like:
(byte-array (mapcat seq my-sequence-of-byte-arrays))
Pregunta
I'm making a function that generates a .wav file. I have the header all set, but I'm running into trouble with the data
itself. I have a function for creating a sine wave at 880Hz (at least I think that's what it does, but that's not my question)--the question is, how do I convert a collection of byte arrays to just one byte array with their contents? This was my best try:
(defn lil-endian-bytes [i]
(let [i (int i)]
(byte-array
(map #(.byteValue %)
[(bit-and i 0x000000ff)
(bit-shift-right (bit-and i 0x0000ff00) 8)
(bit-shift-right (bit-and i 0x00ff0000) 16)
(bit-shift-right (bit-and i 0xff000000) 24)]))))
(def leb lil-endian-bytes)
(let [wr (io/output-stream (str name ".wav") :append true)]
(.write wr
(byte-array (flatten (concat (map
(fn [sample] (leb (* 0xffff (math/sin (+ (* 2 3.14 880) sample)))))
(range (* duration s-rate)) )))))
but it doesn't do what I want it to do: concat all of the byte-arrays into one vector and then into a single byte array. And it makes sense to me why it can't: it can't concat/flatten a byte[] because it's not a vector; it's a byte[]. And it can't cast a byte[] into a byte. But what do I need to do to get this working?
Solución
You might be looking for something like:
(byte-array (mapcat seq my-sequence-of-byte-arrays))
Otros consejos
Converting the byte arrays to be concatenated to sequences and back to byte array may be a little inefficient if you are dealing with large arrays. Here's how to concatenate byte arrays making java.nio.ByteBuffer do the heavy lifting:
(defn concat-byte-arrays [& byte-arrays]
(when (not-empty byte-arrays)
(let [total-size (reduce + (map count byte-arrays))
result (byte-array total-size)
bb (java.nio.ByteBuffer/wrap result)]
(doseq [ba byte-arrays]
(.put bb ba))
result)))
It will be as simple as:
Your byte arrays that needs to be combined in a single byte-array:
(def byte-arrays [(byte-array 10 (byte 1))
(byte-array 10 (byte 2))
(byte-array 10 (byte 3))])
Combine:
(byte-array (for [ar byte-arrays
i ar] i))