I have a pandas DataFrame with multiple measurements per day (for example hourly measurements, but that is not necessarily the case), but I want to keep only the hour for which a certain column is the daily minimum.
My one day in my data frame looks somewhat like this
DATE Value Distance
17 1979-1-2T00:00:00.0 15.5669870447436 34.87
18 1979-1-2T01:00:00.0 81.6306803714536 31.342
19 1979-1-2T02:00:00.0 83.1854759740486 33.264
20 1979-1-2T03:00:00.0 23.8659679630303 32.34
21 1979-1-2T04:00:00.0 63.2755504429306 31.973
22 1979-1-2T05:00:00.0 91.2129044773733 34.091
23 1979-1-2T06:00:00.0 76.493130052689 36.837
24 1979-1-2T07:00:00.0 63.5443183375785 34.383
25 1979-1-2T08:00:00.0 40.9255407683688 35.275
26 1979-1-2T09:00:00.0 54.5583051827551 32.152
27 1979-1-2T10:00:00.0 26.2690011881422 35.104
28 1979-1-2T11:00:00.0 71.3059740399097 37.28
29 1979-1-2T12:00:00.0 54.0111262724049 38.963
30 1979-1-2T13:00:00.0 91.3518048568241 36.696
31 1979-1-2T14:00:00.0 81.7651763485069 34.832
32 1979-1-2T15:00:00.0 90.5695814525067 35.473
33 1979-1-2T16:00:00.0 88.4550315358515 30.998
34 1979-1-2T17:00:00.0 41.6276969038137 32.353
35 1979-1-2T18:00:00.0 79.3818377264749 30.15
36 1979-1-2T19:00:00.0 79.1672568582629 37.07
37 1979-1-2T20:00:00.0 1.48337999844262 28.525
38 1979-1-2T21:00:00.0 87.9110385474789 38.323
39 1979-1-2T22:00:00.0 38.6646421460678 23.251
40 1979-1-2T23:00:00.0 88.4920153764757 31.236
I would like to keep all rows that have the minimum "distance" per day, so for the one day shown above, one would have only one row left (the one with index value 39). I know how to collapse the data frame so that I only have the Distance column left. I can do that - if I first set the DATE as index - with
df_short = df.groupby(df.index.floor('D'))["Distance"].min()
But I also want the Value column in my final result. How do I keep all columns?
It doesn't seem to work if I do
df_short = df.groupby(df.index.floor('D')).min(["Distance"])
This does keep all the columns in the final result, but it seems like the outcome is wrong, so I'm not sure what this does.
Maybe this is already posted somewhere, but I have trouble finding it.
You can use aggregate
df_short = df.groupby(df.index.floor('D')).agg({'Distance': min, 'Value': max})
If you want the kept Value column is the same with minimum of Distance column:
df_short = df.loc[df.groupby(df.index.floor('D'))['Distance'].idxmin(), :]
Make a datetime Index:
df.DATE = pd.to_datetime(df.DATE) # If not already datetime.
df.set_index('DATE', inplace=True)
Resample and find the min Distance's location:
df.loc[df.resample('D')['Distance'].idxmin()]
Output:
Value Distance
DATE
1979-01-02 22:00:00 38.664642 23.251
Related
I have a data frame which I am trying to iterate through, however not based on time, but on an increase of 10 for example
Column A
Column B
12:05
1
13:05
6
14:05
11
15:05
16
so in this case it would return a new data frame with the rows with 1 and 11. How am I able to do this? The different methods that I have tried such as asfreq resample etc. don't seem to work. They say invalid frequency. The reason I think about this is that it is not time based. What is the function that allows me to do this that isn't time based but based on a numerical value such as 10 or 7. I don't want the every nth number, but every time the column value changes by 10 from the last selected value. ex 1 to 11 then if the next values were 12 15 17 21, it would be 21.
here is one way to do it
# do a remainder division, and choose rows where remainder is zero
# offset by the first value, to make calculation simpler
first_val = df.loc[0]['Column B']
df.loc[((df['Column B'] - first_val) % 10).eq(0)]
Column A Column B
0 12:05 1
2 14:05 11
Is there a way to use numpy to add numbers in a series up to a threshold, then restart the counter. The intention is to form groupby based on the categories created.
amount price
0 27 22.372505
1 17 126.562276
2 33 101.061767
3 78 152.076373
4 15 103.482099
5 96 41.662766
6 108 98.460743
7 143 126.125865
8 82 87.749286
9 70 56.065133
The only solutions I found iterate with .loc which is slow. I tried building a solution based on this answer https://stackoverflow.com/a/56904899:
sumvals = np.frompyfunc(lambda a,b: a+b if a <= 100 else b,2,1)
df['cumvals'] = sumvals.accumulate(df['amount'], dtype=np.object)
The use-case is to find the average price of every 75 sold amounts of the thing.
Solution #1 Interpreting the following one way will get my solution below: "The use-case is to find the average price of every 75 sold amounts of the thing." If you are trying to do this calculation the "hard way" instead of pd.cut, then here is a solution that will work well but the speed / memory will depend on the cumsum() of the amount column, which you can find out if you do df['amount'].cumsum(). The output will take about 1 second per every 10 million of the cumsum, as that is how many rows is created with np.repeat. Again, this solution is not horrible if you have less than ~10 million in cumsum (1 second) or even 100 million in cumsum (~10 seconds):
i = 75
df = np.repeat(df['price'], df['amount']).to_frame().reset_index(drop=True)
g = df.index // i
df = df.groupby(g)['price'].mean()
df.index = (df.index * i).astype(str) + '-' + (df.index * i +75).astype(str)
df
Out[1]:
0-75 78.513748
75-150 150.715984
150-225 61.387540
225-300 67.411182
300-375 98.829611
375-450 126.125865
450-525 122.032363
525-600 87.326831
600-675 56.065133
Name: price, dtype: float64
Solution #2 (I believe this is wrong but keeping just in case)
I do not believe you are tying to do it this way, which was my initial solution, but I will keep it here in case, as you haven't included expected output. You can create a new series with cumsum and then use pd.cut and pass bins=np.arange(0, df['Group'].max(), 75) to create groups of cumulative 75. Then, groupby the groups of cumulative 75 and take the mean. Finally, use pd.IntervalIndex to clean up the format and change to a sting:
df['Group'] = df['amount'].cumsum()
s = pd.cut(df['Group'], bins=np.arange(0, df['Group'].max(), 75))
df = df.groupby(s)['price'].mean().reset_index()
df['Group'] = pd.IntervalIndex(df['Group']).left.astype(str) + '-' + pd.IntervalIndex(df['Group']).right.astype(str)
df
Out[1]:
Group price
0 0-75 74.467390
1 75-150 101.061767
2 150-225 127.779236
3 225-300 41.662766
4 300-375 98.460743
5 375-450 NaN
6 450-525 126.125865
7 525-600 87.749286
I am relatively new to this field and am working with a data set to find meaningful insights into customer behavior. My dataset looks like:
customerId week first_trip_week rides
0 156 44 36 2
1 164 44 38 6
2 224 42 36 5
3 224 43 36 4
4 224 44 36 5
What I want to do is create new columns week 44,week 43, week 42 and get the values in the "ride" column to be filled into the rows for the respective customer id. This is in the hope that I can eventually also make the customerId my index and can get denominations for different weeks. Help would be greatly appreciated!
Thank you!!
If I'm understanding you correctly, you want to create new columns in the same dataframe for weeks 44, 43, and 42 with the correct values for each customerId and NaN for those that don't have it. If your original dataframe has all the user data, I would first filter for dataframes that have the correct week number
week42DF = dataset.loc[dataset['week']==42,['customerId','rides']].rename(columns={'rides':'week42Rides'})
getting only the rides and customerId and renaming the former here to make things a little easier for us. Then left join the old dataframe and the new one on customerId
dataset = pd.merge(dataset,week42DF,how='left',on='customerId')
The users that are missing from week42DF will have NaN in the week42rides column in the merged dataset which you can then use the .fillna(0) method to replace with zeros. Do this for each week you require.
See Pandas' documentation on merge and the more general concatenate for more info.
I have a data frame. I have grouped a column status by date using
y = news_dataframe.groupby(by=[news_dataframe['date'].dt.date,news_dataframe['status']])['status'].count()
and my output is --
date status count
2019-05-29 selected 24
rejected auto 243
waiting 109
no action 1363
2019-05-30 selected 28
rejected auto 188
waiting 132
no action 1249
repeat 3
2019-05-31 selected 13
rejected auto 8
waiting 23
no action 137
repeat 2
source 1
Name: reasonForReject, dtype: int64
Now I want to calculate the percentage of each status group by date. How can I achieve this using pandas dataframe?
Compute two different groupbys and divide one by the other:
y_numerator = news_dataframe.groupby(by=[news_dataframe['date'].dt.date,news_dataframe['status']])['status'].count()
y_denominator = news_dataframe.groupby(by=news_dataframe['date'].dt.date)['status'].count()
y=y_numerator/y_denominator
I guess that's the shortest:
news_dataframe['date'] = news_dataframe['date'].dt.date
news_dataframe.groupby(['date','status'])['status'].count()/news_dataframe.groupby(['date'])['status'].count()
try this:
# just fill the consecutive rows with this
df=df.ffill()
df.df1.columns=['date','status','count']
# getting the total value of count with date and status
df1=df.groupby(['date']).sum().reset_index()
#renaming it to total as it is the sum
df1.columns=['date','status','total']
# now join the tables to find the total and actual value together
df2=df.merge(df1,on=['date'])
#calculate the percentage
df2['percentage']=(df2.count/df2.total)*100
If you need one liner its:
df['percentage']=(df.ffill()['count]/df.ffill().groupby(['date']).sum().reset_index().rename(columns={'count': 'total'}).merge(df,on=['date'])['total'])*100
The rolling function in Pandas can only calculate rolling statistics according to row counts or date/time columns. But I want to have a discrete time column for calculating rolling sum, something like this:
key time value
A 1 10
A 2 20
A 4 30
A 7 10
B 1 15
B 2 30
B 3 15
I want to first group by key, then calculate the rolling sum on value for the nearest 3 time:
key time value output
A 1 10 10
A 2 20 30(10+20)
A 4 30 60(10+20+30)
A 7 10 40(30+10)
B 1 15 15
B 2 30 45
B 3 15 60
I tried this:
grouped = input.groupby("key", as_index=False)
for name, group in grouped:
group = group.sort_values("time")
time = list(group["time"])
value = list(group["value"])
#calcRollingStat is a custom function that outputs a list of corresponding results
out = calcRollingStat(time, value, mode="avg")
group["output"] = out #out is a list
But then I don't know how to convert grouped back to DataFrame. Pandas tells me that there is no reset_index attribute in grouped.
Is my code the best method to do this? How would you tackle this problem?
Thank you!
I believe you can use GroupBy.apply with custom function:
def f(group):
group = group.sort_values("time")
time = list(group["time"])
value = list(group["value"])
#calcRollingStat is a custom function that outputs a list of corresponding results
group["output"] = calcRollingStat(time, value, mode="avg")
return group
df = input.groupby("key", as_index=False).apply(f)