# Finding aggregated information of data

I am new to data science. I have a dataset of around 200,000 records, having 5 columns. There is a field called, class. For each class, there are one or many divisions. I have to do this: 1. Filter the dataset, such that only those classes with at least 5 divisions turn up.

1. For each division, I have to calculate attendance from another column.

2. There is a minimum attendance value for each class. I have to find the percentage of divisions in each class with the minimum attendance.

I started with importing the data in python using Pandas and started writing loops for processing this. But I am sure this is not the right way to do. Can you please give some idea.Can I do this in Excel pivot table?

• In r, data.table and dplyr packages will do that. – user227710 Jun 23 '15 at 23:36

Take a look at map(),reduce(),filter() functions in Python.

It is a bit hard to solve your problem without data but I tried to give it a go with a how I think the data would be encoded. I used R with data.tables. You can read data.tables with fread().

# Step 1

 require(data.table)

# Assume sample_data has the following format:
#   class: the class
#   division: the division
#   attendance: the attandance for a match
#
# I assume the table is in long format e.g. multiple rows exist per class with
# per class one or different divisions.

# Make the list of classes with at least 5 divisions.
classes_of_interest <-
sample_data[,
.(num_divisions = length(unique(divisions))),
by = class][num_divisions > 4, class]


# Step 2

 # Only consider the classes that were in at least 5 divisions.
attandance_by_division <-
sample_data[class %in% classes_of_interest,
.(attendance = sum(num_people)),
by = list(division, class)]
setkey(attandance_by_division, "class")


# Step 3

 # Merge the data set with a datas set that contains the required number
# of attendants per class.
# The  format is as follows:
#   class: the class
#   mininum_attendance: the minimum attendance
attendance_data <-
merge(attendance_requirements,
attandance_by_division, by = "class")

# Here I exploit the fact that the true/false condition will be converted
# to a 1 and 0. So I can sum and divide by the length of index subset created
# by aggregating on 'class'.
pct_of_division <-
sample_data[,
.(pct_with_min_attendance = (sum(attendance > minimum_attendance)
/ length(.I))),
by = class]


Hope this helps