I am trying to split a copy off of a Pandas dataframe starting after a certain column by header name.
So far, I've been able to manipulate the column headers or indexes according to a set number of known columns, like below. However, the number of columns will change, and I want to still extract every column that happens after.
In the below example, say I want to grab all columns after 'Tail' even if the 'Body' columns goes to column X. So the below sample with X number of Body columns:
df = pd.DataFrame({'Intro1': ['blah'],
'Intro2': ['blah'],'Intro3': ['blah'],'Body1': ['blah'],'Body2': ['blah'],'Body3': ['blah'],'Body4': ['blah'], ... 'BodyX': ['blah'],'Tail': ['blah'],'OtherTail': ['blah'],'StillAnotherTail': ['blah'],})
Should produce a copy of the dataframe as:
dftail = pd.DataFrame({'Tail': ['blah'],'OtherTail': ['blah'],'StillAnotherTail': ['blah'],})
Ideally I'd like to find a way to combine the two techiques below so that the column starts at 'Tail' and goes to the end of the dataframe:
dftail = [col for col in df if col.startswith('Tail')]
dftail = df.iloc[:, 164:] # column number (164) will change based on 'Tail' index number
How about this:
df_tail = df.iloc[:, list(df.columns).index("Tail"):]
df_tail then prints out:
Tail OtherTail StillAnotherTail
0 blah blah blah
Related
I I have a Pyspark dataset with a column “channels” that looks like this:
channels
name1,name2,name3,name4
happy1,happy2
entity1,entity2,entity3,entity4,entity5
I want to create 5 new columns i.e “channel1, channel2, channel3, channel4, channel5”.
Then, I want to split the contents of the “channels” column using the comma separator. After splitting values from each row, I want to put each separated value in a different column.
For example for the first row, the columns should look like this:
channel1 channel2 channel3 channel4 channel5
name1 name2 name3 name4 ~
When an element is not found, i want to use ~ as the column value. For example in the first row, there were only 4 values instead of 5 so for the channel5 column, I used ~
I only want to use ~, not None or NULL.
How can I achieve this result in pyspark?
I tried this:
df = df.withColumn("channels_split", split(df["channels"], ","))
df = df.withColumn("channel1", coalesce(df["channels_split"][0], "~"))
df = df.withColumn("channel2", coalesce(df["channels_split"][1], "~"))
df = df.withColumn("channel3", coalesce(df["channels_split"][2], "~"))
df = df.withColumn("channel4", coalesce(df["channels_split"][3], "~"))
df = df.withColumn("channel5", coalesce(df["channels_split"][4], "~"))
df = df.drop("channels_split")
but it gives me an error that:
`~` is missing
You're referencing the column `~`, but it is missing from the schema. Please check your code.
Note that I am using pyspark within Foundry
Coalesce expects cols as arguments and you are providing String, i think that you should use lit("~")
https://spark.apache.org/docs/latest/api/python/reference/pyspark.sql/api/pyspark.sql.functions.coalesce.html
This is more of a spark problem than a Foundry problem though.
What #M_S said is correct, as the error message was stating, you need a column and should use the lit function.
But be careful if
spark.sql.ansi.enabled is set to True
then this code will throw an ArrayIndexOutOfBoundsException if there are less than 5 items in your array.
Another way to do this would be to ensure that your array has at least 5 elements on each row by adding some ~, then get the first 5 items or by adding a temporary column with the length of the array and use a when condition.
By the way, you don't need to repeat df = every time
df = (
df
.withColumn("channels_split", split(df["channels"], ","))
.withColumn("default_values", array_repeat(lit("~"), 5)))
.withColumn("channels_split", concat(col("channels_split"), col("default_values")))
.withColumn("channel1", df["channels_split"][0])
.withColumn("channel2", df["channels_split"][1])
.withColumn("channel3", df["channels_split"][2])
.withColumn("channel4", df["channels_split"][3])
.withColumn("channel5", df["channels_split"][4])
.drop("channels_split")
)
I have a big data set with tons of rows. I have one column in that data set with long row values. I want to rename these row values with shorter names and use the previous column values as a part of name. How can I do this without dictionary and list in Pandas. Because I cannot put every single value in a dict.
I have a dataset like this:
enter image description here
And I want something like this output:
enter image description here
I create a DF with random long strings inside. I see you actually don't use them in the result.
df['Col2'] = df.groupby('Col1').cumcount()+1
df['Col2'] = df['Col1'] + '-U' + df['Col2'].astype('str')
df
I have a pandas dataframe like this:
How do I get the price of an item1 without making 'Items column' an index column?
I tried df['Price (R)'][item1] but it returns the price of item2, while I expect output to be 1
The loc operators are required in front of the selection brackets []. When using loc, the part before the comma is the rows you want, and the part after the comma is the columns you want to select. Therefore, the code can be:
result = df.loc[df['Items']=="item1","Price(R)"]
The data type of created output is Pandas Series object.
I don't even know if groupby is the correct function to use for this. It's a bit hard to understand so Ill include a screenshot of my dataframe: screenshot
Basically, this dataframe has way too many columns because each column is specific to only one or a few rows. You can see in the screenshot that the first few columns are specific towards the first row and the last few columns are specific to the last row. I want to make it so that each row only has the columns that actually pertain to it. I've tried several methods of using groupby('equipment name') and several methods using dropna but none work in the way I need it to. I'm also open to separating it into multiple dataframes.
Any method is acceptable, this bug has been driving me crazy. It took me a while to get to this point because this started out as an unintelligible 10,000 line json. I'm pretty new to programming as well.
This is a very cool answer that could be one option - and it does use groupby so sorry for dismissing!!! This will group your data into DataFrames where each DataFrame has a unique group of columns, and any row which only contains values for those columns will be in that DataFrame. If your data are such that there are multiple groups of rows which share the exact same columns, this solution is ideal I think.
Just to note, though, if your null values are more randomly spread out throughout the dataset, or if one row in a group of rows is missing a single entry (compared to related rows), you will end up with more combinations of unique non-null columns, and then more output DataFrames.
There are also (in my opinion) nice ways to search a DataFrame, even if it is very sparse. You can check the non-null values for a row:
df.loc[index_name].dropna()
Or for an index number:
df.iloc[index_number].dropna()
You could further store these values, say in a dictionary (this is a dictionary of Series, but could be converted to DataFrame:
row_dict = {row : df.loc[row].dropna() for row in df.index}
I could imagine some scenarios where something based off these options is more helpful for searching. But that linked answer is slick, I would try that.
EDIT: Expanding on the answer above based on comments with OP.
The dictionary created in the linked post contain the DataFrames . Basically you can use this dictionary to do comparisons with the original source data. My only issue with that answer was that it may be hard to search the dictionary if the column names are janky (as it looks like in your data), so here's a slight modification:
for i, (name,df) in enumerate(df.groupby(df.isnull().dot(df.columns))):
d['df' + str(i)] = df.dropna(1)
Now the dictionary keys are "df#", and the values are the DataFrames. So if you wanted to inspect the content one DataFrame, you can call:
d['df1'].head()
#OR
print(d['df0'])
If you wanted to look at all the DataFrames, you could call
for df in d.values():
print(df.head()) #you can also pass an integer to head to show more rows than 5
Or if you wanted to save each DataFrame you could call:
for name in sorted(d.keys()):
d[name].to_csv('path/to/file/' + name + '.csv')
The point is, you've gotten to a data structure where you can look at the original data, separated into DataFrames without missing data. Joining these back into a single DataFrame would be redundant, as it would create a single DataFrame (equal to the original) or multiple with some amount of missing data.
I think it comes down to what you are looking for and how you need to search the data. You could rename the dictionary keys / output .CSV files based on the types of machinery inside, for example.
I thought your last comment might mean that objects of similar type might not share the same columns; say for example if not all "Exhaust Fans" have the same columns, they will end up in different DataFrames in the dictionary. This maybe the type of case where it might be easier to just look at individual rows, rather than grouping them into weird categories:
df_dict = {row : pd.DataFrame(df.loc[row].dropna()).transpose() for row in df.index}
You could again then save these DataFrames as CSV files or look at them one by one (or e.g. search for Exhaust Fans by seeing if "Exhaust" is in they key). You could also print them all at once:
import pandas as pd
import numpy as np
import natsort
#making some randomly sparse data
columns = ['Column ' + str(i+1) for i in range(10)]
index = ['Row ' + str(i+1) for i in range(100)]
df = pd.DataFrame(np.random.rand(100,10), columns=columns,index=index)
df[df<.7] = np.nan
#creating the dictionary where each key is a row name
df_dict = {row : pd.DataFrame(df.loc[row].dropna()).transpose() for row in df.index}
#printing all the output
for key in natsort.natsorted(df_dict.keys())[:5]: #using [:5] to limit output
print(df_dict[key], '\n')
Out[1]:
Column 1 Column 4 Column 7 Column 9 Column 10
Row 1 0.790282 0.710857 0.949141 0.82537 0.998411
Column 5 Column 8 Column 10
Row 2 0.941822 0.722561 0.796324
Column 2 Column 4 Column 5 Column 6
Row 3 0.8187 0.894869 0.997043 0.987833
Column 1 Column 7
Row 4 0.832628 0.8349
Column 1 Column 4 Column 6
Row 5 0.863212 0.811487 0.924363
Instead of printing, you could write the output to a text file; maybe that's the type of document that you could look at (and search) to compare to the input tables. Bute not that even though the printed data are tabular, they can't be made into a DataFrame without accepting that there will be missing data for rows which don't have entries for all columns.
I have 3 series which is generated out of the code shown below. I have shown a the code for one series below
I would like to merge 3 such series/dataframes using columns (subject_id,hadm_id,icustay_id) but unfortunately these headings don't appear as column names. How do I convert them as columns and use them for merging with another series/dataframe of similar datatype
I am generating series from another dataframe (df) based on the condition given below. Though I already tried converting this series to dataframe, still it doesn't display the indices, instead it displays the column name as index. I have shown the output below. I would like to see the values 'Subject_id','hadm_id','icustay_id' as column names in dataframe along with other column 'val_bw_80_110' so that I can join with other dataframes using these 3 ids ('Subject_id','hadm_id','icustay_id')
s1 =
df.groupby(['subject_id','hadm_id','icustay_id'['val_bw_80_110'].mean()
I expect an output where the ids (subject_id,hadm_id,icustay_id) are converted to column names and can be used for joining/merging with other dataframes.
You can add parameter as_index=False to DataFrame.groupby or use Series.reset_index:
df = df.groupby(['subject_id','hadm_id','icustay_id'], as_index=False)['val_bw_80_110'].mean()
Or:
df = df.groupby(['subject_id','hadm_id','icustay_id'])['val_bw_80_110'].mean().reset_index()