Sample.kt

val audioRecordAdapter = ItemAdapter(data)

val sections = mutableListOf<Section>()
sections.add(DateSection(0, "Today"))
sections.add(DateSection(2, "15/05/2016"))

val customSectionAdapter = CustomSectionAdapter()
customSectionAdapter.configSections(sections)

val sectionAdapter = SectionedRecyclerViewAdapter(customSectionAdapter, audioRecordAdapter)

recyclerView.adapter = sectionAdapter

Section.kt

/**
 * Base class that represents the position
 * of the Section on the RecyclerView.
 */
open class Section(val firstPosition: Int, var sectionedPosition: Int = 0)

SectionAdapter.kt

/**
 * This class represents the base implementation
 * of the section. To use this you need to extends
 * your class and inflate and bind your data like
 * a {@link #RecyclerView.Adapter}.
 */
abstract class SectionAdapter: RecyclerView.Adapter<RecyclerView.ViewHolder>() {

  var sections : SparseArray<Section> = SparseArray()

  override fun getItemCount() = sections.size()

  fun configSections(sections: List<Section>) {
    this.sections.clear()
    sections.sortedWith(Comparator { lhs, rhs ->
      if (lhs.firstPosition == rhs.firstPosition) 0
      else if (lhs.firstPosition < rhs.firstPosition) -1
      else 1
    })
    var offset = 0
    sections.forEach {
      it.sectionedPosition = it.firstPosition + offset
      this.sections.append(it.sectionedPosition, it)
      ++offset
    }
  }

}

SectionedRecyclerViewAdapter.kt

package com.tpro.ui.helper.sectionRecyclerView

import android.support.v7.widget.RecyclerView
import android.view.ViewGroup
import com.tpro.ui.adapter.viewType.SectionedType

class SectionedRecyclerViewAdapter(
    val sectionAdapter: SectionAdapter,
    val itemAdapter: RecyclerView.Adapter<RecyclerView.ViewHolder>):
    RecyclerView.Adapter<RecyclerView.ViewHolder>() {

  private var valid = true

  init {
    itemAdapter.registerAdapterDataObserver(object : RecyclerView.AdapterDataObserver() {

      override fun onChanged() {
        toggleValid()
        notifyDataSetChanged()
      }

      override fun onItemRangeChanged(positionStart: Int, itemCount: Int) {
        toggleValid()
        notifyItemRangeChanged(positionStart, itemCount)
      }

      override fun onItemRangeInserted(positionStart: Int, itemCount: Int) {
        toggleValid()
        notifyItemRangeInserted(positionStart, itemCount)
      }

      override fun onItemRangeRemoved(positionStart: Int, itemCount: Int) {
        toggleValid()
        notifyItemRangeRemoved(positionStart, itemCount)
      }
    })
  }

  override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int): RecyclerView.ViewHolder? {
    return when(viewType) {
      SectionedType.HEADER.value -> sectionAdapter.onCreateViewHolder(parent, viewType)
      else -> itemAdapter.onCreateViewHolder(parent, viewType - 1)
    }
  }

  override fun onBindViewHolder(holder: RecyclerView.ViewHolder?, position: Int) {
    if (isSectionHeaderPosition(position)) {
      sectionAdapter.onBindViewHolder(holder, position)
    } else {
      itemAdapter.onBindViewHolder(holder, sectionedPositionToPosition(position))
    }
  }

  override fun getItemViewType(position: Int) =
      if (isSectionHeaderPosition(position))
        SectionedType.HEADER.value
      else itemAdapter.getItemViewType(sectionedPositionToPosition(position)) + 1

  override fun getItemId(position: Int) =
      if(isSectionHeaderPosition(position))
      (Integer.MAX_VALUE - sectionAdapter.sections.indexOfKey(position)).toLong() else
        itemAdapter.getItemId(sectionedPositionToPosition(position))

  override fun getItemCount() = if(valid) itemAdapter.itemCount + sectionAdapter.itemCount else 0

  fun toggleValid() = itemAdapter.itemCount > 0

  fun positionToSectionedPosition(position: Int): Int {
    var offset = 0
    for (i in 0..sectionAdapter.sections.size() - 1) {
      if (sectionAdapter.sections.valueAt(i).sectionedPosition > position) {
        break
      }
      ++offset
    }
    return position + offset
  }

  fun sectionedPositionToPosition(sectionedPosition: Int): Int {
    if (isSectionHeaderPosition(sectionedPosition)) {
      return RecyclerView.NO_POSITION
    }
    var offset = 0
    for (i in 0..sectionAdapter.sections.size() - 1) {
      if (sectionAdapter.sections.valueAt(i).sectionedPosition > sectionedPosition) {
        break
      }
      --offset
    }
    return sectionedPosition + offset
  }

  fun isSectionHeaderPosition(position: Int)= sectionAdapter.sections.get(position) != null

}

SectionedType.kt

/**
 * Type of item on RecyclerView. Used
 * by the adapter.
 */
enum class SectionedType(val value: Int) { HEADER(0), ITEM(1) }

Warning

Are you using ProGuard? Use this:

The files above are localized inside the folder `com.myProject.ui.helper`, 
then you need to do something similar of this:

-dontwarn com.myProject.ui.helper.sectionRecyclerView.**
-keep class com.myProject.ui.helper.sectionRecyclerView.** { *; }
-keep interface com.myProject.ui.helper.sectionRecyclerView.** { *; }

Where is ItemAdapter(data) class?