Graph Lines Disappear in Certain Frames of Animation

I’ve got a Dash graph “animation” (multiple frames, which show different days) whose lines don’t show up when the frame changes. I’ve been using Dash for a few years now and I’ve never run into this problem before, but I have a reproducible example below.

Here’s what all of the frames are supposed to look like (note the red lines on top and purple lines on the bottom):
enter image description here

That was the first frame, above. The second frame from the right looks like this, with no red lines above the purple lines. I can assure you there’s data there; it’s just not showing up! Check for yourself with the output from print(tabulate()).
enter image description here

To get set up to answer this question, install the following libraries:

pip install dash flask plotly pandas colour tabulate

There’s no perfect way to share a rather large DataFrame, but sharing text is preferable to providing a download link (thanks @vestland for the tip from his answer here).

Here’s the full code, ready for you to copy and paste, and see the “bug”:

from flask import Flask
import dash
import dash_core_components as dcc
import dash_html_components as html
import plotly.graph_objects as go
import pandas as pd
from colour import Color
from tabulate import tabulate


# Create the "list_of_dicts" for Pandas
list_of_dicts = [
    {
        "Unnamed: 0": 1499,
        "timestamp_local": "2021-01-19 20:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 6.33,
        "up_down": "Downstroke",
        "hour": 20,
        "load": -241.0,
    },
    {
        "Unnamed: 0": 21615,
        "timestamp_local": "2021-01-19 20:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 6.33,
        "up_down": "Upstroke",
        "hour": 20,
        "load": 165.9,
    },
    {
        "Unnamed: 0": 1687,
        "timestamp_local": "2021-01-19 20:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 6.73,
        "up_down": "Downstroke",
        "hour": 20,
        "load": -239.0,
    },
    {
        "Unnamed: 0": 21803,
        "timestamp_local": "2021-01-19 20:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 6.73,
        "up_down": "Upstroke",
        "hour": 20,
        "load": 147.76,
    },
    {
        "Unnamed: 0": 1875,
        "timestamp_local": "2021-01-19 20:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 7.13,
        "up_down": "Downstroke",
        "hour": 20,
        "load": -242.0,
    },
    {
        "Unnamed: 0": 21991,
        "timestamp_local": "2021-01-19 20:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 7.13,
        "up_down": "Upstroke",
        "hour": 20,
        "load": 128.0,
    },
    {
        "Unnamed: 0": 2063,
        "timestamp_local": "2021-01-19 20:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 7.53,
        "up_down": "Downstroke",
        "hour": 20,
        "load": -244.0,
    },
    {
        "Unnamed: 0": 22179,
        "timestamp_local": "2021-01-19 20:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 7.53,
        "up_down": "Upstroke",
        "hour": 20,
        "load": 109.25,
    },
    {
        "Unnamed: 0": 2251,
        "timestamp_local": "2021-01-19 20:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 7.94,
        "up_down": "Downstroke",
        "hour": 20,
        "load": -243.0,
    },
    {
        "Unnamed: 0": 22367,
        "timestamp_local": "2021-01-19 20:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 7.94,
        "up_down": "Upstroke",
        "hour": 20,
        "load": 92.6206896551724,
    },
    {
        "Unnamed: 0": 1500,
        "timestamp_local": "2021-01-19 21:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 6.33,
        "up_down": "Downstroke",
        "hour": 21,
        "load": -245.0,
    },
    {
        "Unnamed: 0": 21616,
        "timestamp_local": "2021-01-19 21:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 6.33,
        "up_down": "Upstroke",
        "hour": 21,
        "load": 183.84615384615384,
    },
    {
        "Unnamed: 0": 1688,
        "timestamp_local": "2021-01-19 21:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 6.73,
        "up_down": "Downstroke",
        "hour": 21,
        "load": -244.0,
    },
    {
        "Unnamed: 0": 21804,
        "timestamp_local": "2021-01-19 21:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 6.73,
        "up_down": "Upstroke",
        "hour": 21,
        "load": 163.5,
    },
    {
        "Unnamed: 0": 1876,
        "timestamp_local": "2021-01-19 21:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 7.13,
        "up_down": "Downstroke",
        "hour": 21,
        "load": -244.0,
    },
    {
        "Unnamed: 0": 21992,
        "timestamp_local": "2021-01-19 21:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 7.13,
        "up_down": "Upstroke",
        "hour": 21,
        "load": 145.44444444444446,
    },
    {
        "Unnamed: 0": 2064,
        "timestamp_local": "2021-01-19 21:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 7.53,
        "up_down": "Downstroke",
        "hour": 21,
        "load": -246.0,
    },
    {
        "Unnamed: 0": 22180,
        "timestamp_local": "2021-01-19 21:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 7.53,
        "up_down": "Upstroke",
        "hour": 21,
        "load": 128.21052631578948,
    },
    {
        "Unnamed: 0": 2252,
        "timestamp_local": "2021-01-19 21:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 7.94,
        "up_down": "Downstroke",
        "hour": 21,
        "load": -246.0,
    },
    {
        "Unnamed: 0": 22368,
        "timestamp_local": "2021-01-19 21:00:00-07:00",
        "timestamp_local_day": "2021-01-19 00:00:00-07:00",
        "inches": 7.94,
        "up_down": "Upstroke",
        "hour": 21,
        "load": 110.55555555555556,
    },
    {
        "Unnamed: 0": 1315,
        "timestamp_local": "2021-01-20 16:00:00-07:00",
        "timestamp_local_day": "2021-01-20 00:00:00-07:00",
        "inches": 6.05,
        "up_down": "Downstroke",
        "hour": 16,
        "load": -202.0,
    },
    {
        "Unnamed: 0": 21431,
        "timestamp_local": "2021-01-20 16:00:00-07:00",
        "timestamp_local_day": "2021-01-20 00:00:00-07:00",
        "inches": 6.05,
        "up_down": "Upstroke",
        "hour": 16,
        "load": 176.0,
    },
    {
        "Unnamed: 0": 1503,
        "timestamp_local": "2021-01-20 16:00:00-07:00",
        "timestamp_local_day": "2021-01-20 00:00:00-07:00",
        "inches": 6.45,
        "up_down": "Downstroke",
        "hour": 16,
        "load": -204.0,
    },
    {
        "Unnamed: 0": 21619,
        "timestamp_local": "2021-01-20 16:00:00-07:00",
        "timestamp_local_day": "2021-01-20 00:00:00-07:00",
        "inches": 6.45,
        "up_down": "Upstroke",
        "hour": 16,
        "load": 166.0,
    },
    {
        "Unnamed: 0": 1691,
        "timestamp_local": "2021-01-20 16:00:00-07:00",
        "timestamp_local_day": "2021-01-20 00:00:00-07:00",
        "inches": 6.85,
        "up_down": "Downstroke",
        "hour": 16,
        "load": -202.0,
    },
    {
        "Unnamed: 0": 21807,
        "timestamp_local": "2021-01-20 16:00:00-07:00",
        "timestamp_local_day": "2021-01-20 00:00:00-07:00",
        "inches": 6.85,
        "up_down": "Upstroke",
        "hour": 16,
        "load": 154.0,
    },
    {
        "Unnamed: 0": 1879,
        "timestamp_local": "2021-01-20 16:00:00-07:00",
        "timestamp_local_day": "2021-01-20 00:00:00-07:00",
        "inches": 7.25,
        "up_down": "Downstroke",
        "hour": 16,
        "load": -202.0,
    },
    {
        "Unnamed: 0": 21995,
        "timestamp_local": "2021-01-20 16:00:00-07:00",
        "timestamp_local_day": "2021-01-20 00:00:00-07:00",
        "inches": 7.25,
        "up_down": "Upstroke",
        "hour": 16,
        "load": 142.0,
    },
    {
        "Unnamed: 0": 2067,
        "timestamp_local": "2021-01-20 16:00:00-07:00",
        "timestamp_local_day": "2021-01-20 00:00:00-07:00",
        "inches": 7.66,
        "up_down": "Downstroke",
        "hour": 16,
        "load": -202.0,
    },
    {
        "Unnamed: 0": 22183,
        "timestamp_local": "2021-01-20 16:00:00-07:00",
        "timestamp_local_day": "2021-01-20 00:00:00-07:00",
        "inches": 7.66,
        "up_down": "Upstroke",
        "hour": 16,
        "load": 130.0,
    },
]

# Create the DataFrame from the list_of_dicts
df = pd.DataFrame(list_of_dicts)
df = df.sort_values(["timestamp_local", "inches", "up_down"])

# For viewing and verifying DataFrame contents in VS Code:
print(df["timestamp_local"].unique())
print(
    tabulate(
        df[["timestamp_local", "inches", "up_down", "hour", "load"]],
        headers="keys",
        tablefmt="psql",
    )
)

#############################################################################
# Create the animation in Plotly-Dash
frames = []
slider_steps = []
slider_distinct_days_set = set()

mode = "lines"
marker = dict(
    size=5,
    opacity=0.5,
)
line = dict(
    shape="spline",
    smoothing=0.4,
)

# Transition in milliseconds for the animation (default 500)
duration_frame = 1000
duration_transition = 0
duration_transition_slider = 1000

# Docs say redraw not needed for scatterplots, but if it doesn't redraw,
# the annotations stay the same as for the first frame...
redraw = True

easing = "exp-in-out"
ordering = "layout first"  # default
mode_animate = "immediate"  # default

bootstrap_blue_base = Color("blue")
bootstrap_blue_lum = Color("blue")
bootstrap_blue_lum.luminance = 0.8

bootstrap_red_base = Color("red")
bootstrap_red_lum = Color("red")
bootstrap_red_lum.luminance = 0.8

# Add scatters to the animation by day
for gname_day, gdf_day in df.groupby("timestamp_local_day"):
    frame = {"data": [], "name": gname_day, "layout": {}}

    hours_in_day = gdf_day["timestamp_local"].nunique()
    up_colors = list(bootstrap_red_lum.range_to(bootstrap_red_base, hours_in_day))
    down_colors = list(bootstrap_blue_lum.range_to(bootstrap_blue_base, hours_in_day))

    for gname_isup, gdf_isup in gdf_day.groupby("up_down"):
        i = 0
        colors = down_colors if gname_isup == "Downstroke" else up_colors
        for label, gdf_ts in gdf_isup.groupby("timestamp_local"):
            print(f"{gname_day} {gname_isup} {label} color: {colors[i].hex}")
            frame["data"].append(
                go.Scatter(
                    name=label,
                    mode=mode,  # lines or markers
                    x=gdf_ts["inches"],
                    y=gdf_ts["load"],
                    marker=dict(
                        color=colors[i].hex,
                    ),
                    line=line,
                )
            )
            i += 1

    frames.append(frame)

    if gname_day not in slider_distinct_days_set:
        slider_distinct_days_set.add(gname_day)
        slider_steps.append(
            {
                "method": "animate",
                "label": gname_day,  # text label to appear on the slider
                "args": [
                    [gname_day],
                    {
                        "mode": mode_animate,
                        "frame": {"duration": duration_frame, "redraw": redraw},
                        "transition": {
                            "duration": duration_transition_slider,
                            "easing": easing,
                        },
                        "ordering": ordering,
                    },
                ],
            }
        )

most_recent_day_available_index = max(0, len(slider_distinct_days_set) - 1)
sliders = [
    {
        # IMPORTANT: this is the "active" step in the slider, which shows up on load
        "active": most_recent_day_available_index,
        "pad": {"b": 10, "t": 60},
        "len": 0.9,
        "x": 0.1,
        "xanchor": "left",
        "y": 0,
        "yanchor": "top",
        "steps": slider_steps,
        "transition": {"duration": duration_transition_slider},
    }
]

updatemenus = [
    {
        "type": "buttons",
        "direction": "left",
        "pad": {"r": 10, "t": 70},
        "showactive": False,
        "x": 0.1,
        "xanchor": "right",
        "y": 0,
        "yanchor": "top",
        "buttons": [
            {
                "label": "Play",
                "method": "animate",
                "args": [
                    None,
                    {
                        "mode": mode_animate,
                        "direction": "reverse",  # forward or reverse
                        "fromcurrent": True,
                        "frame": {"duration": duration_frame, "redraw": redraw},
                        "transition": {
                            "duration": duration_transition,
                            "easing": easing,
                        },
                        "ordering": ordering,
                    },
                ],
            },
            {
                "label": "Pause",
                "method": "animate",
                "args": [
                    [None],
                    {
                        "mode": "immediate",
                        "frame": {"duration": 0, "redraw": redraw},
                        "transition": {
                            "duration": 0,
                        },
                    },
                ],
            },
        ],
    }
]

fig = go.Figure(
    # Make the initial data, before the animation frames start
    data=frames[-1]["data"],
    frames=frames,
    layout=go.Layout(
        hovermode="closest",
        height=500,
        plot_bgcolor="white",
        showlegend=False,
        font={"family": "Segoe UI", "color": "#717174"},
        xaxis=dict(
            gridcolor="rgb(238,238,238)",
            range=[6, 8],
            title="position",
        ),
        yaxis=dict(
            gridcolor="rgb(238,238,238)",
            range=[-350, 350],
            title="Weight",
        ),
        margin=go.layout.Margin(l=0, r=10, b=0, t=0),
        sliders=sliders,
        updatemenus=updatemenus,
    ),
)

external_stylesheets = ["https://codepen.io/chriddyp/pen/bWLwgP.css"]


def create_app():
    app = Flask(__name__)
    dashapp = dash.Dash(__name__, server=app, external_stylesheets=external_stylesheets)

    dashapp.layout = html.Div(
        [
            dcc.Graph(
                figure=fig,
            )
        ]
    )

    return app


app = create_app()

if __name__ == "__main__":
    app.run(debug=True, host="0.0.0.0", port=5000)

The problem/bug is described in the Plotly-Dash animations documentation here:

Animations are designed to work well when each row of input is present across all animation frames, and when categorical values mapped to symbol, color and facet are constant across frames. Animations may be misleading or inconsistent if these constraints are not met.

My example has daily frames, but each day does not have the same number of hours of data. Jan 19 has two hours, while Jan 20 only has one hour.

To fix the problem, I need to make each day have the same number of hourly “charts” (e.g. 24 charts of data each day).

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