16 Data: Slice & Dice

• There are multiple ways to slice and dice dataframe
• Indexing could be done at both row level and column level

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16.1 R

Set the working directory to the data folder and read the iris dataset as an R object DF.

DF = read.csv('iris.csv')

Approach	Explanation	Example
Select row(s)
[i, ]	Get the row indexed by integer value i	DF[, 4]
Name	Get the row by name	DF[c('3', '4'), ]
[-i, ]	Remove the row indexed by integer value i	DF[-3, ]
logical operator	Get the rows where condition is TRUE (note incomplete length will recycle)	DF[DF$SepalLength >= 7.5, ]
Select column(s)
$	Get the named column	DF$Species
[, j]	Get the column indexed by integer value j	DF[, 4]
Name	Get the column by name string	DF['Species']; DF[, c('SepalLength', 'Species')]
[, -j]	Remove the column indexed by integer value j	DF[, -4]
logical operator	Get the columns where the condition is TRUE (note incomplete length will recycle)	DF[,c(T,F,F,F,T)]

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16.2 Python

Set the working directory to the data folder and read the iris dataset as an R object DF.

import pandas as pd

DF = pd.read_csv('iris.csv')

Remember: For Python, the indexing starts at zero and the operation at row or column level is according to

start, stop, step format.

Approach	Explanation	Example
Select row(s)
iloc[index]	Get the row(s) by the index value (index-based location)	DF.iloc[10, ]; DF.iloc[0:10, ]; DF.iloc[0:10:2, ]
logical operator	Get the rows where condition is TRUE (note incomplete length will recycle)	DF[DF.SepalLength >= 7.5, ]
drop with axis 0	Drop the indexed rows	DF.drop([0,1], axis = 0)
Select column(s)
.	Get the named column	DF.Species
[Name]	Get the named column	DF['Species']; DF[:, ['SepalLength', 'Species']]
loc[:, Name]	Get the named column (name-based location)	DF.loc[:, ['Species']]; DF.loc[:, ['SepalLength', 'Species']]; DF.loc[:, 'SepalWidth':'Species']
drop with axis 1	Drop the named columns	DF.drop(['SepalLength', 'Species'], axis = 1)

DF = read.csv('./data/iris.csv')

DF[, 4]
DF[c(3, 4), ]

DF[-3, ]

DF[DF$SepalLength >= 7.5, ]

DF$Species
DF[, 4]

DF['Species']

DF[[, c('SepalLength', 'Species')]
   
DF[, -4]

DF[,c(T,F,F,F,T)]