如何解决如何访问 lua 表中的值？
我有以下 lua 代码可以打印出设备的 Mac 地址。
local sc = Command.Scan.create()
local devices = sc:scan()
local topicMac
local list = {}
for _,device in pairs(devices) do
print(device:getMACAddress())
list[device] = device:getMACAddress()
end
topicMac = list[0]
print(topicMac)
由于有多个地址并且它们列在一个表中，我只想将第一个保存到局部变量“topicMac”中。我尝试通过在数组中添加第一个索引（0 或 1）来达到第一个值。
为什么我得到 nil 作为回报？
解决方法
Future <DataSnapshot> getData()async{
List lists = [];
await databaseReference.once().then((DataSnapshot snapshot) {
Map < dynamic,dynamic > values = snapshot.value;
values.forEach((key,values)async {
await FirebaseDatabase.instance.reference().child("Users/" + values["UID"].toString() + "/Name").once().then((DataSnapshot snapshot) {
lists.add(snapshot.value);
print(snapshot.value);
}); },);
}
);
print(lists);
}
关键字可以用作变体函数来检索表中的第一个索引和值
next所以在你的情况下：
local index,value = next(tab) -- returns the first index and value of a table
“First”和“Second”取决于我们拥有的键。要检查它，只需使用 print():
import dash
import dash_bootstrap_components as dbc
from dash.dependencies import Input,Output,State
import dash_core_components as dcc
import dash_html_components as html
import plotly.graph_objs as go
from plotly.subplots import make_subplots
import plotly.express as px
card_content1_1 = [
dbc.CardHeader([dbc.Row([html.H5("SALES VOLUME TREND",className = "font-weight-bold text-success"),dbc.Button(
html.I(className="fa fa-window-maximize"),color="success",id="sales_maximize",className="ml-auto",# href="www.cogitaas.com"
)
])]),dbc.CardBody(
[dcc.Graph(
id='sales_graph',figure={},style={'height':'30vh'}
# className="mt-5"
)])]
card_stacked_discount = [
dbc.CardHeader([dbc.Row([html.H5("VOLUMES UNDER DIFFERENT DISCOUNT LEVELS",className="font-weight-bold text-info text-center"),color="info",id="discount_maximize",dbc.CardBody(
[dcc.Dropdown(
id = 'stacked_discount_dropdown',options =stacked_discount_options,value=stacked_discount_options[0].get('value'),style={'color':'black'},# multi=True
),dcc.Graph(
id='stacked_discount_graph',style={'height':'30vh'}
)])]
cards = html.Div(
[
dbc.Row(
[
dbc.Col(dbc.Card(card_content1_1,outline=True,style={'height':'auto'}),width=8),],className="mb-4",),dbc.Row(
[
dbc.Col(dbc.Card(card_stacked_discount,outline=True),dbc.Col(dbc.Card([
dbc.Row([
dbc.Col(dbc.Card(disc_sub_title,inverse=True)),]),html.Br(),dbc.Row([
dbc.Col(dbc.Card(disc_sub_card1,outline=True)),width=4)
],]
)
tab1_content = dbc.Card(
dbc.CardBody(
[cards,]
),className="mt-3",)
tabs = dbc.Tabs(dbc.Tab(tab1_content,label="Data",label_style={'color':'blue'},tab_style={"margin-left":"auto"}),])
content = html.Div([
html.Div([tabs]),id="page-content")
app.layout = html.Div([dcc.Location(id="url"),content])
@app.callback(
dash.dependencies.Output('sales_graph','figure'),[dash.dependencies.Input('platform-dropdown','value'),dash.dependencies.Input('signature-dropdown',dash.dependencies.Input('franchise-dropdown',dash.dependencies.Input('sales_maximize','n_clicks'),dash.dependencies.Input('time-dropdown',])
def update_sales_graph(plat,sign,fran,maximize,time_per):
print(str(time_per)+"Test")
time_ax=[]
if isinstance(time_per,str):
time_ax.append(time_per)
time_per=time_ax
if (time_per==None) or ('Full Period' in (time_per)):
dff = df[(df.Platform==plat) & (df.Signature==sign) & (df.Franchise==fran)]
elif ('YTD' in time_per):
dff = df[(df.Platform == plat) & (df.Signature == sign) & (df.Franchise == fran) & (df.year==2020)]
else:
dff = df[(df.Platform==plat) & (df.Signature==sign) & (df.Franchise==fran) & (df.Qtr_yr.isin(time_per))]
fig = px.area(dff,x='Date',y='Qty_Orig',color_discrete_sequence=px.colors.qualitative.Dark2)
fig.add_trace(go.Scatter(x=dff['Date'],y=dff['Outliers'],mode = 'markers',name='Outliers',line=dict(color='darkblue')))
fig.add_trace(go.Scatter(x=dff['Date'],y=dff['bestfit'],name='Long Term Trend',line=dict(color='darkblue')))
fig.update_layout(font_family="Rockwell",title={'text': fran + " Volume Trend",'y': 0.99,# 'x': 0.15,# 'xanchor': 'auto','yanchor': 'top'
},legend=dict(
orientation="h",# y=-.15,yanchor="bottom",x=0.5,xanchor="center"
),yaxis_visible=False,yaxis_showticklabels=False,xaxis_title=None,margin=dict(l=0,r=0,t=0,b=0,pad=0),plot_bgcolor='White',paper_bgcolor='White',)
fig.update_xaxes(showgrid=False,zeroline=True)
fig.update_yaxes(showgrid=False,zeroline=True)
changed_id = [p['prop_id'] for p in dash.callback_context.triggered][0]
if 'maximize' in changed_id:
fig.show()
return fig
@app.callback(
dash.dependencies.Output('stacked_discount_graph',dash.dependencies.Input('discount_maximize',dash.dependencies.Input('stacked_discount_dropdown',])
def stacked_discount(plat,sales_days,time_per):
time_ax=[]
if isinstance(time_per,str):
time_ax.append(time_per)
time_per=time_ax
# else:
# time_per=list(time_per)
if (time_per==None) or ('Full Period' in (time_per)):
df_promo = df_promo_vol[(df_promo_vol.Platform==plat) & (df_promo_vol.Signature==sign) & (df_promo_vol.Franchise==fran)]
elif ('YTD' in time_per):
df_promo = df_promo_vol[(df_promo_vol.Platform == plat) & (df_promo_vol.Signature == sign) & (df_promo_vol.Franchise == fran) & (df_promo_vol.Year==2020)]
else:
df_promo = df_promo_vol[(df_promo_vol.Platform==plat) & (df_promo_vol.Signature==sign) & (df_promo_vol.Franchise==fran) & (df_promo_vol.Qtr_yr.isin(time_per))]
color_discrete_map = {
"0 - 10": "orange","10 - 15": "green","15 - 20": "blue","20 - 25": "goldenrod","25 - 30": "magenta","30 - 35": "red","35 - 40": "aqua","40 - 45": "violet","45 - 50": "brown","50 + ": "black"
}
category_orders = {'disc_range': ['0 - 10','10 - 15','15 - 20','20 - 25','25 - 30','30 - 35','35 - 40','40 - 45','45 - 50','50 + ']}
if (sales_days == None) or (sales_days == 'sales_act'):
fig = px.bar(df_promo,x='start',y='units_shipped',color='disc_range',color_discrete_map=color_discrete_map,category_orders=category_orders,)
else:
fig = px.bar(df_promo,y='Date',color="disc_range",)
fig.update_layout(font_family="Rockwell",title={'text': fran + " Sales Decomposition",'x': 0.1,# yaxis_visible=False,t=30,b=30,zeroline=True)
changed_id = [p['prop_id'] for p in dash.callback_context.triggered][0]
if 'maximize' in changed_id:
fig.show()
return fig
如果键是数字，您可以决定哪个是“第一个”。如果键是字符串，您仍然可以使用算法来确定表中的第一项：
for k,d in pairs(devices) do
print(k,' = ',d:getMACAddress())
end
如果键是对象或函数，则不能直接比较它们。所以你必须选择任何第一项：
local the_first = "some_default_key"
for k,d in pairs(devices) do
if k < the_first then -- or use custom function: if isGreater(the_first,k) then
the_first = k
end
end
topicMac = devices[the_first]:getMACAddress()
print(topicMac)
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