Notes

Some basic Python summary

Some basic SQL code summary

Four main points for a qualified data analyst should be able to do.

Leetcode problems about string

Couple of leetcode problems related to linked list

Use stack to tackle this type of matching problem

Basic data type: Double String Logic If the items are not of the same type, they are coerced: string <-- numeric <-- logical negative indexes (used for exclusion) Automatic vector extension makes vectors very different from matrices and arrays, for which automatic extension does not exist. Lists are sequences of anything. They can contain: basic data types, vectors, matrices, arrays, lists (recursion),… Create a vector consisting of the numbers 1 to N, where 1 appears once, 2 appears twice, 3 appears 3 times,… rep(1:x, 1:x) Reshape vector into a matrix in two ways (arranged by row and column) matrix(0:1, nrow=3, ncol=4, byrow=T) # if want to arrange by column, just without the "byrow" part [,1] [,2] [,3] [,4] [1,] 0 1 0 1 [2,] 0 1 0 1 [3,] 0 1 0 1 Select rows of a matrix in R that meet a condition car_models <- ``c``(``'Maruti'``,``'Hyundai'``,``'Tata'``, ``'Ford'``,``'Nissan'``,``'Toyota'``) car_type <- ``c``(``'Diesel'``,``'Petrol'``,``'Petrol'``, ``'Diesel'``,``'Petrol'``,``'Diesel'``) car_color <- ``c``(``'Red'``,``'Blue'``,``'Red'``, ``'Red'``,``'Blue'``,``'Red'``) year <- ``c``(2001,2011,2013,2012,2021,2021) # Storing matrix in mat (variable) mat <- ``cbind``(car_models,car_type,car_color,year) # condition to select only rows with # color = Red mat <- mat[mat[,``"car_color"``]==``"Red"``,] # displaying the resultant matrix mat car_models car_type car_color year [1,] "Maruti" "Diesel" "Red" "2001" [2,] "Tata" "Petrol" "Red" "2013" [3,] "Ford" "Diesel" "Red" "2012" [4,] "Toyota" "Diesel" "Red" "2021"