install.packages(tidyverse)Packages & reading/writing data
Learning Objectives
1.) How to install and load libraries
2.) How to view and inspect data
3.) Read in data files & output data (write to file)
R Basics
Installing and Loading libraries
Libraries are packages of functions (and sometimes data) that we use to execute tasks in R. Packages are what make R so versatile! We can do almost anything with R if we learn how to utilize the right packages.
If we do not have a package already installed (for example, if you have only just downloaded R/ RStudio), we will need to use install.packages(‘packagename’) to install each package that we need.
OR - We can use the ‘Packages’ tab in the bottom right quadrant to install packages. Simply navigate to ‘Packages’, select ‘install packages’ and enter the package names you need (separate each package by commas). NOTE for users for rstudio.mtholyoke.edu – You cannot install packages to the Mt Holyoke cloud instance of R. If we need something that isn’t installed we will need to contact IT!
In order for a package to work, we must first load it! We do this as with the code libary(packagename)
library(tidyverse) #for data manipulation
library(palmerpenguins) #for some fun data!It is best practice to load all of the packages you will need at the top of your script
In this course we will be following a best practices guide that utilizes a library called ‘Tidyverse’ for data manipulation and analysis. Tidyverse contains many packages all in one, including the very functional ‘dplyr’ and ‘ggplot2’ packages. You will almost always use Tidyverse, so make sure to load it in :)
Note the ‘#’ with notes after them in the code chunk above. These are called comments. You can comment out any line of code in R by using a ‘#’. This is strongly recommended when you are programming. We will discuss more later!
Looking at data!
R has integrated data sets that we can use to play around with code and learn.
examples: mtcars (a dataframe all about cars, this is available in R without loading a package), and iris (in the ‘vegan’ package, great for testing out ecology related functions and code)
Load a dataset R has some test datasets built into it. Let’s load one and look at it!
mtcars mpg cyl disp hp drat wt qsec vs am gear carb
Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
Hornet 4 Drive 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1
Hornet Sportabout 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2
Valiant 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1
Duster 360 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4
Merc 240D 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2
Merc 230 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2
Merc 280 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4
Merc 280C 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4
Merc 450SE 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3
Merc 450SL 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3
Merc 450SLC 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3
Cadillac Fleetwood 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4
Lincoln Continental 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4
Chrysler Imperial 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4
Fiat 128 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1
Honda Civic 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2
Toyota Corolla 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1
Toyota Corona 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1
Dodge Challenger 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2
AMC Javelin 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3 2
Camaro Z28 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3 4
Pontiac Firebird 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2
Fiat X1-9 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1
Porsche 914-2 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2
Lotus Europa 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2
Ford Pantera L 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5 4
Ferrari Dino 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6
Maserati Bora 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5 8
Volvo 142E 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2Using head() and tail() Now let’s look at the data frame (df) using head() and tail()
These tell us the column names, and let us see the top or bottom 6 rows of data.
head(mtcars) mpg cyl disp hp drat wt qsec vs am gear carb
Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4
Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4
Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1
Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1
Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2
Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1tail(mtcars) #tail shows the header and the last 6 rows mpg cyl disp hp drat wt qsec vs am gear carb
Porsche 914-2 26.0 4 120.3 91 4.43 2.140 16.7 0 1 5 2
Lotus Europa 30.4 4 95.1 113 3.77 1.513 16.9 1 1 5 2
Ford Pantera L 15.8 8 351.0 264 4.22 3.170 14.5 0 1 5 4
Ferrari Dino 19.7 6 145.0 175 3.62 2.770 15.5 0 1 5 6
Maserati Bora 15.0 8 301.0 335 3.54 3.570 14.6 0 1 5 8
Volvo 142E 21.4 4 121.0 109 4.11 2.780 18.6 1 1 4 2column attributes If we want to see the attributes of each column we can use the str() function
str(mtcars) #str shows attributes of each column'data.frame': 32 obs. of 11 variables:
$ mpg : num 21 21 22.8 21.4 18.7 18.1 14.3 24.4 22.8 19.2 ...
$ cyl : num 6 6 4 6 8 6 8 4 4 6 ...
$ disp: num 160 160 108 258 360 ...
$ hp : num 110 110 93 110 175 105 245 62 95 123 ...
$ drat: num 3.9 3.9 3.85 3.08 3.15 2.76 3.21 3.69 3.92 3.92 ...
$ wt : num 2.62 2.88 2.32 3.21 3.44 ...
$ qsec: num 16.5 17 18.6 19.4 17 ...
$ vs : num 0 0 1 1 0 1 0 1 1 1 ...
$ am : num 1 1 1 0 0 0 0 0 0 0 ...
$ gear: num 4 4 4 3 3 3 3 4 4 4 ...
$ carb: num 4 4 1 1 2 1 4 2 2 4 ...str() is very important because it allows you to see the type of data in each column. Types include: integer, numeric, factor, date, and more. If the data in a column are factors instead of numbers you may have an issue in your data (your spreadsheet)
Changing column attributes Importantly, you can change the type of the column. Here is an example
mtcars$mpg=as.factor(mtcars$mpg) # Makes mpg a factor instead of a number
str(mtcars)'data.frame': 32 obs. of 11 variables:
$ mpg : Factor w/ 25 levels "10.4","13.3",..: 16 16 19 17 13 12 3 20 19 14 ...
$ cyl : num 6 6 4 6 8 6 8 4 4 6 ...
$ disp: num 160 160 108 258 360 ...
$ hp : num 110 110 93 110 175 105 245 62 95 123 ...
$ drat: num 3.9 3.9 3.85 3.08 3.15 2.76 3.21 3.69 3.92 3.92 ...
$ wt : num 2.62 2.88 2.32 3.21 3.44 ...
$ qsec: num 16.5 17 18.6 19.4 17 ...
$ vs : num 0 0 1 1 0 1 0 1 1 1 ...
$ am : num 1 1 1 0 0 0 0 0 0 0 ...
$ gear: num 4 4 4 3 3 3 3 4 4 4 ...
$ carb: num 4 4 1 1 2 1 4 2 2 4 ...mtcars$mpg=as.numeric(as.character(mtcars$mpg)) #Changes mpg back to a number
str(mtcars)'data.frame': 32 obs. of 11 variables:
$ mpg : num 21 21 22.8 21.4 18.7 18.1 14.3 24.4 22.8 19.2 ...
$ cyl : num 6 6 4 6 8 6 8 4 4 6 ...
$ disp: num 160 160 108 258 360 ...
$ hp : num 110 110 93 110 175 105 245 62 95 123 ...
$ drat: num 3.9 3.9 3.85 3.08 3.15 2.76 3.21 3.69 3.92 3.92 ...
$ wt : num 2.62 2.88 2.32 3.21 3.44 ...
$ qsec: num 16.5 17 18.6 19.4 17 ...
$ vs : num 0 0 1 1 0 1 0 1 1 1 ...
$ am : num 1 1 1 0 0 0 0 0 0 0 ...
$ gear: num 4 4 4 3 3 3 3 4 4 4 ...
$ carb: num 4 4 1 1 2 1 4 2 2 4 ...Summary statistics To see summary statistics on each column (mean, median, min, max, range), we can use summary()
summary(mtcars) #summarizes each column mpg cyl disp hp
Min. :10.40 Min. :4.000 Min. : 71.1 Min. : 52.0
1st Qu.:15.43 1st Qu.:4.000 1st Qu.:120.8 1st Qu.: 96.5
Median :19.20 Median :6.000 Median :196.3 Median :123.0
Mean :20.09 Mean :6.188 Mean :230.7 Mean :146.7
3rd Qu.:22.80 3rd Qu.:8.000 3rd Qu.:326.0 3rd Qu.:180.0
Max. :33.90 Max. :8.000 Max. :472.0 Max. :335.0
drat wt qsec vs
Min. :2.760 Min. :1.513 Min. :14.50 Min. :0.0000
1st Qu.:3.080 1st Qu.:2.581 1st Qu.:16.89 1st Qu.:0.0000
Median :3.695 Median :3.325 Median :17.71 Median :0.0000
Mean :3.597 Mean :3.217 Mean :17.85 Mean :0.4375
3rd Qu.:3.920 3rd Qu.:3.610 3rd Qu.:18.90 3rd Qu.:1.0000
Max. :4.930 Max. :5.424 Max. :22.90 Max. :1.0000
am gear carb
Min. :0.0000 Min. :3.000 Min. :1.000
1st Qu.:0.0000 1st Qu.:3.000 1st Qu.:2.000
Median :0.0000 Median :4.000 Median :2.000
Mean :0.4062 Mean :3.688 Mean :2.812
3rd Qu.:1.0000 3rd Qu.:4.000 3rd Qu.:4.000
Max. :1.0000 Max. :5.000 Max. :8.000 Counting rows and columns To see the number of rows and columns we can use nrow() and ncol()
nrow(mtcars) #gives number of rows[1] 32ncol(mtcars) #gives number of columns[1] 11Naming dataframes Rename mtcars and view in Environment tab in Rstudio
a<-mtcars
a mpg cyl disp hp drat wt qsec vs am gear carb
Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
Hornet 4 Drive 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1
Hornet Sportabout 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2
Valiant 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1
Duster 360 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4
Merc 240D 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2
Merc 230 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2
Merc 280 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4
Merc 280C 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4
Merc 450SE 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3
Merc 450SL 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3
Merc 450SLC 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3
Cadillac Fleetwood 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4
Lincoln Continental 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4
Chrysler Imperial 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4
Fiat 128 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1
Honda Civic 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2
Toyota Corolla 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1
Toyota Corona 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1
Dodge Challenger 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2
AMC Javelin 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3 2
Camaro Z28 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3 4
Pontiac Firebird 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2
Fiat X1-9 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1
Porsche 914-2 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2
Lotus Europa 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2
Ford Pantera L 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5 4
Ferrari Dino 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6
Maserati Bora 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5 8
Volvo 142E 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2head(a) mpg cyl disp hp drat wt qsec vs am gear carb
Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4
Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4
Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1
Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1
Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2
Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1Write data to file (saving data)
We use the write.csv function here. a= the name of the dataframe and the name we want to give the file goes after ‘file=’
The file name must be in quotes and must include an extension. Since we are using write.csv we MUST use .csv
write.csv(a, file='mtcars.csv')Read a file in (import data into R)
NOTE: if you have a .xls file make sure you convert to .csv. Ensure the file is clean and orderly (rows x columns). Only 1 excel tab can be in each .csv, so plan accordingly. Note that in order to read a file in to R from your computer (or cloud server), that file MUST be located within your working directory (or you must know and enter the file path).
IF your file is in your working directory, you can read it in like this:
b<-read.csv('mtcars.csv')
head(b) X mpg cyl disp hp drat wt qsec vs am gear carb
1 Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4
2 Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4
3 Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1
4 Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1
5 Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2
6 Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1You are welcome to use other functions to read in data (including read_csv or read.xls). Especially for beginners, I strongly encourage you to use .csv format. Other file formats can get complicated (often unnecessarily complicated). That said, R can also handle .txt, .xls, images, shapefiles (for spatial analysis or GIS style work), etc. It is very versatile! Feel free to explore :)
A note on read_csv -> I consider this to be the “best” option for reading in .csv files. It is a ‘smarter’ version of read.csv and can automatically figure out what kind of data (numeric, factor, date, etc) each column is. If you use read.csv, you have often have to manually change these options.
Read a file from an online source
In some cases you may be using data you’ve found online. Perhaps you can download, save, and then read your file into R. Sometimes that is more work than we want to do. You can just call a file directly from it’s URL. Here is an example:
I have a dataframe on coral cover from Belize that I want to read in. It is located on my github coral cover data. Let’s read it directly into R! The URL you see above is NOT what we use in R. If you find a file on Github you want to locate the ‘raw’ version of the file. To do this:
1.) Click the link above (or find a data file on github)
2.) Navigate to the top right menu and look for the box that says “Raw” in it. You can click on that and open the raw file and then copy the URL. OR, you can click the box next to the “Raw” box to copy the link to the raw file. We use this link to read our data into R. This will work for any .csv you find on github. I like to get practice data from the TidyTuesday project on Github. You can find their data at the following link:
Tidy Tuesday Data
coralcover<- read_csv('https://raw.githubusercontent.com/jbaumann3/BIOL234_Biostats_MHC/main/coralcover.csv')Rows: 77 Columns: 6
── Column specification ────────────────────────────────────────────────────────
Delimiter: ","
chr (1): type
dbl (5): site, lat, transect, diver, cc_percent
ℹ Use `spec()` to retrieve the full column specification for this data.
ℹ Specify the column types or set `show_col_types = FALSE` to quiet this message.head(coralcover)# A tibble: 6 × 6
site type lat transect diver cc_percent
<dbl> <chr> <dbl> <dbl> <dbl> <dbl>
1 1 Back Reef 3 1 4 5.84
2 1 Back Reef 3 2 4 0.951
3 1 Back Reef 3 3 4 5.24
4 1 Back Reef 3 4 5 5.00
5 1 Back Reef 3 5 5 5.90
6 2 Patch Reef 3 1 4 5.28