today i begin learning R LOL
no choice, gotta pick it up for work. i guess it’s always good to learn more languages!
i begin by searching for a python/r cheatsheet - this is pretty good for a quick peek into the differences in the syntax:
this is more indepth (in particular basic R gives an interesting overview): http://www.datasciencefree.com/cheatsheets.html
but for now…i need some real (basic) practice. datacamp, here i come!
most important takeaways so far:
R BEGINS WITH INDEX 1 INSTEAD OF 0!!! faints.
vector <- c(x, y, z) creates a vector, and assigns it to vector. 1:9 is a shortcut for creating a vector from 1 to 9.
name(vector) names the parts of the vector! interesting.
selection of x[1:5] INCLUDES both 1 and 5
matrix(1:9, byrow = TRUE, nrow = 3) constructs a 3 row matrix from the vector 1:9, filled in by rows (instead of by columns)
colnames(matrix), rownames(matrix) can be used to name the matrix
cbind(matrix, vector) can be used to join matrices/vectors n vectors together.
rbind(matrix, matrix) are for two matrices
factor(vector) changes it to a factor, and by changing the level(factor), you can change all the names (e.g. M,F to Male, Female)!!! homg
summary(factor) is the equivalent of .describe(), summary(vector) gives info about the length, type, etc
factor_speed_vector <- factor(speed_vector, ordered=TRUE, levels=c(‘slow’, ‘medium’, ‘fast’)) this creates an ordinal factor, levels is the correct order.
str(dataframe) gives the structure of the df head(dataframe) is equivalent to pandas df.head()
data.frame(x, y, z) creates a df
dataframe$col selects the col
subset(dataframe, subset = x < 1) selects the rows where x<1
use position <- order(df$col) to get the positions sorted by col, then df[position,] to get the sorted list
list(x, y, z) to create lists
list[] to select first element from list
list[[‘actors’]] selects the second element in the actors col
RStudio is like, the equivalent of Jupyter Notebook (I think!)
Download R, and then download RStudio.
as a start to actually get coding, and then trying stuff out on the Titanic Dataset.
install.packages(‘packagename’) is like the equivalent of pip install
if you come across the ‘tar: failed to set default locale error’, use the solution here: https://stackoverflow.com/questions/3907719/how-to-fix-tar-failed-to-set-default-locale-error
so i’m trying to do a
df.isnull().sum() in R…
after a bit of a search,
sapply(df, function(x) sum(is.na(x))) or
map(df, ~sum(is.na(.))) seems the cleanest - the former requires no dependencies, the latter needs tidyverse. also i like the former’s format a little better…
here’s a summary: https://sebastiansauer.github.io/sum-isna/
also, if NA for your string is represented by ‘’, remember to add
na.strings = '' when reading it in!
seq() is the equivalent of range()
rep(vector, times = 2) repeats the vector by the number of times, entirely. changing times to each repeats each element in the vector several times first, before going to the next element
is.*() checks for type
as.*() converts it to type e.g. as.data.table() but need to import library(data.table)
rev() reverses the order
grepl(patterns = regex, x = string) search for regex in the string, returns logical
grep() returns indices instead
sub() replaces the first match
gsub() replaces all
Sys.Date() returns a date object, today’s date Sys.time() current time as.Date() to convert
learning dplyr: select, mutate, filter, arrange, summarize
names(df) is the equivalent of df.columns n() gives the length of the df
df_less <- df %>% select(df, 1:5, -2) # select columns 1 to 5, excluding 2. df_lesser <- df %>% select(df, year, country, lifeExp:pop) # select columns by name
helper functions in select:
starts_with(“X”); ends_with(“X”); contains(“X”);
matches(“X”) “X” can be a regular expression;
num_range(“x”, 1:5) this gives the variables named x01, x02, x03, x04 and x05;
one_of(x): every name that appears in x, which should be a character vector.
library(dplyr) df %>% # pipes this result into the first argument in the next step filter(year == 1990, country == "United States") # to filter rows arrange(desc(year)) # to arrange mutate(lifeExpMonths = lifeExp * 12) # to create a new column by_year_continent <- df %>% # assign the result to a variable filter(year <= 1990) %>% group_by(continent, year) %>% # group by summarize(meanLifeExp = mean(lifeExp), # to summarize totalPop = sum(pop))
library(ggplot2) # scatterplots ggplot(df, aes(x = pop, y = gdpPercap, color = continent, size = pop)) + # color and size geom_point() + # geom_point is scatterplot scale_x_log10() + # puts x on log scale. if y, just use scale_y_log10() expand_limits(x=0) # sets x axis to start at 0 # subplots ggplot(df, aes(x = pop, y = gdpPercap, color = continent, size = pop)) + # color and size geom_point() + facet_wrap(~ continent) # creates subplots by continent
to plot a line plot, change
geom_histogram(binwidth = 5)
to add title:
connecting to mysql
Set up a connection to the mysql database my_db <- src_mysql(dbname = “dplyr”, host = “courses.xxx.us-east-1.rds.amazonaws.com”, port = 3306, user = “student”, password = “xxx”)
Reference a table within that source: df df <- tbl(my_db, “dplyr”)
model <- lm(y ~ x, data = df) summary(model)
tidying data up
library(broom) # to tidy up the results from summary, turns model into a df tidy(model) bind_rows(tidy(model1), tiday(model2)) # combine results into one big df
library(tidyr) nested <- by_year_country %>% nest(-country) %>% # nest all except country column, into a data column (is a list). there is a tibble (df) for each country unnest(data) # brings it back up to the same level
to retrieve one of the nested data, use indexing:
library(purrr) by_year_country %>% nest(-country) %>% mutate(models = map(data, ~ lm(percent_yes ~ year, .))) %>% # map applies function to all items in the list. in this case the function is a linear model mutate(tidied = map(models,tidy)) %>% # tidies the models unnest(tidied) # unnest the tidied models