Basic of basic
print |
no need any other exp |
exponentiation |
^ |
modulo |
%% |
assignment |
= or <- |
equal sign |
== |
case sensitive |
YES |
or |
| |
double operators |
&&, || only examine 1st elements in vectors |
Factor
factor() |
2 types |
nominal vs. ordinal |
Data structures
vector |
c() one dim-array, same data type, arithmetic calculations OK, names() |
matrix |
two dim-array, same data type, arithmetic calculations OK |
data frame |
two dim-object, different data types |
list |
1 dim object, different data types |
df is a list where each element is a column so df[[col]] equals column
FUNCTION
fun <- function(arg1, arg2) {...} |
3 elements: arguments, body, environment |
return() stop execution and return a value, used to return early for special cases not routinely |
functions are objects |
descriptive, use consistent naming convention, no overriding existing object names, data args come first |
functions can be arguments to other functions --> functional programming |
pipe operator: %>% |
safely(), possibly(), quietly() - handling errors |
side effects: beyond the results of a function, i.e. print output, plot, save files to disk |
3 main problems: type-unstable functions( [, sapply), non-standard evaluation, hidden arguments |
stop("error msg", call. = FALSE) |
view global options: options(), getOption("digits") |
purr - map(), map_dbl(), map_int(), etc. apply the same function to a list. Similar to the apply family - sapply(), lapply()
map2(.x, .y, .f, ...), pmap(.l, .f, ...) - multiple args
invoke_map(.f, .x = list(NULL), ...) - multiple functions
walk() similar to map() but for side effects
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Basic functions
class() |
str() |
rbind(), cbind() |
colSums(), rowSums(), nrow(), ncol() |
data.frame(), subset() |
order(), arrange(), rank() |
file.path() |
return file path |
seq_along() |
generate sequence for "for loop" can handle empty cases |
Subsetting
starts from 1 |
[2:5] equals to |
c(2,3,4,5) |
df[ ,1] |
1st column |
df[1, ] |
1st row |
df[2,3] |
2nd row & 3rd column |
df$x |
select element name x |
ls[x] vs. ls[[x]] or $ |
sublist vs. element |
IF Syntax
if (condition1) {
ex1
} else if (condition2) {
ex2
} else {
ex3
}
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FOR syntax
for (i in list) {
print(i)
}
for (i in 1:length(list)) {
print(list[[i]])
}
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break & next
break - abandons the active loop: the remaining code in the loop is skipped and the loop is not iterated over anymore.
next - skips the remainder of the code in the loop, but continues the iteration. |
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Importing data
read.csv(), read.delim() |
read.csv2(), read.delim2() - local diff. in decimal convention |
read.table("foo.txt", header = TRUE, sep = "/", stringsAsFactors = FALSE) |
readxl - read_excel("foo.xlsx", sheet=bar); lapply(excel_sheets("foo.xlsx"), read_excel, path = "foo.xlsx") |
XLConnect - loadWorkbook(), getSheets(), readWorksheet() & a lots more |
read SQL - DBI, dbListTables, dbReadTable, dbGetQuery(efficient!) |
read JSON - jsonlite: fromJSON() |
read stats. software - haven, foreign |
packages: readr - similar to utils but simpler; data.table:fread - fast, convenient
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