A course in quantitative research workflow for students in the higher education administration program at the University of Florida
This supplemental lesson is a companion to the lesson on data wrangling with Tidyverse. While the tidyverse has fundamentally changed the way many people work with R, you can still use base or “vanilla” R for your data wrangling tasks. You may find it useful to perform an example data analysis without the support of the tidyverse.
Because much of the material is otherwise the same, we won’t go into the same depth in this supplemental lesson (you’ll even see some repeated text). We’ll simply work to answer the research question posed in the other lesson.
Let’s imagine we’ve been given the following data analysis task with the HSLS09 data:
Figure out average differences in college degree expectations across census regions; for a first pass, ignore missing values and use the higher of student and parental expectations if an observation has both.
A primary skill (often unremarked upon) in data analytic work is translation. Your advisor, IR director, funding agency director — even collaborator — won’t speak to you in the language of R. Instead, it’s up to you to (1) translate a research question into the discrete steps coding steps necessary to provide an answer, and then (2) translate the answer such that everyone understands what you’ve found.
What we need to do is some combination of the following:
Let’s do it!
NOTE: Since we’re not using the tidyverse, we don’t need to call it this time. Even with non-tidyverse R, you may need to call libraries. This analysis, however, does not require any.
## ---------------------------
## libraries
## ---------------------------
## NONE
This script — like the one from the organizing
lesson — assumes that the
scripts subdirectory is the working directory, that the required
data file is in the data subdirectory, and that both subdirectories
are at the same level in the course directory. Like this:
student_skinner/ <--- Top-level
|
|__/data <--- Sub-level 1
| |--+ hsls_small.csv
|
|__/scripts <--- Sub-level 1 (Working directory)
|--+ dw_one_base_r.R
If you need a refresher on setting the working directory, see the prior lesson.
Notice that I’m not setting (i.e. hard coding) the working directory in the script. That would not work well for sharing the code. Instead, I tell you where you need to be (a common landmark), let you get there, and then rely on relative paths afterwards.
## ---------------------------
## directory paths
## ---------------------------
## assume we're running this script from the ./scripts subdirectory
dat_dir <- file.path("..", "data")
For this lesson, we’ll use a subset of the High School Longitudinal Study of 2009 (HSLS09), an IES / NCES data set that features:
- Nationally representative, longitudinal study of 23,000+ 9th graders from 944 schools in 2009, with a first follow-up in 2012 and a second follow-up in 2016
- Students followed throughout secondary and postsecondary years
- Surveys of students, their parents, math and science teachers, school administrators, and school counselors
- A new student assessment in algebraic skills, reasoning, and problem solving for 9th and 11th grades
- 10 state representative data sets
If you are interested in using HSLS09 for future projects, DO NOT rely on this subset. Be sure to download the full data set with all relevant variables and weights if that’s the case. But for our purposes in this lesson, it will work just fine.
Throughout, we’ll need to consult the code book. An online version can be found at this link (after a little navigation).
Quick exercise
Follow the code book link above in your browser and navigate to the HSLS09 code book.
## ---------------------------
## input
## ---------------------------
## data are CSV, so we use read.csv(), which is base R function
df <- read.csv(file.path(dat_dir, "hsls_small.csv"))
Unlike the read_csv() function we’ve used before, read.csv()
(notice the difference: a . instead of an _) doesn’t print
anything. So that we can see our data, well print to the
console. BUT before we do that…
read.csv() returns a base R data.frame() rather than the special
data frame or tibble() that the tidyverse uses. It’s mostly the
same, but one difference is that whereas R will only print the
first 10 rows of a tibble, it will print the entire data.frame. We
don’t need to see the whole thing, so we’ll use the head() function
to print only the first 10 rows.
## show first 10 rows
head(df, n = 10)
## stu_id x1sex x1race x1stdob x1txmtscor x1paredu x1hhnumber x1famincome
## 1 10001 1 8 199502 59.3710 5 3 10
## 2 10002 2 8 199511 47.6821 3 6 3
## 3 10003 2 3 199506 64.2431 7 3 6
## 4 10004 2 8 199505 49.2690 4 2 5
## 5 10005 1 8 199505 62.5897 4 4 9
## 6 10006 2 8 199504 58.1268 3 6 5
## 7 10007 2 8 199409 49.4960 2 2 4
## 8 10008 1 8 199410 54.6249 7 3 7
## 9 10009 1 8 199501 53.1875 2 3 4
## 10 10010 2 8 199503 63.7986 3 4 4
## x1poverty185 x1ses x1stuedexpct x1paredexpct x1region x4hscompstat
## 1 0 1.5644 8 6 2 1
## 2 1 -0.3699 11 6 1 1
## 3 0 1.2741 10 10 4 1
## 4 0 0.5498 10 10 3 1
## 5 0 0.1495 6 10 3 1
## 6 0 1.0639 10 8 3 -8
## 7 0 -0.4300 8 11 1 1
## 8 0 1.5144 8 6 1 1
## 9 0 -0.3103 11 11 3 1
## 10 0 0.0451 8 6 1 -8
## x4evratndclg x4hs2psmos
## 1 1 3
## 2 1 3
## 3 1 4
## 4 0 -7
## 5 0 -7
## 6 -8 -8
## 7 1 2
## 8 1 3
## 9 1 8
## 10 -8 -8
Quick exercise
read.csv()is special version ofread.table(), which can read various delimited file types, that is, tabular data in which data cells are separated by a special character. What’s the special character used to separate CSV files? Once you figure it out, re-read in the data usingread.table(), being sure to set thesepargument to the correct character.
You’ll also notice that the data.frame doesn’t tell use the types of
our columns. If we really want to know, we can use the class()
function. So that we can see all columns, we can use the sapply()
function, which will let us apply the class() function across all
columns.
## show column types
sapply(df, class)
## stu_id x1sex x1race x1stdob x1txmtscor x1paredu
## "integer" "integer" "integer" "integer" "numeric" "integer"
## x1hhnumber x1famincome x1poverty185 x1ses x1stuedexpct x1paredexpct
## "integer" "integer" "integer" "numeric" "integer" "integer"
## x1region x4hscompstat x4evratndclg x4hs2psmos
## "integer" "integer" "integer" "integer"
Data frames are like special matrices. They have rows and columns. You
can access these rows and columns using square bracket notation
([]). Because a matrix has two dimensions, you use a comma inside
the square brackets to indicate what you mean ([,]):
df[<rows>,<cols>]At it’s most basic, you can use numbers to represent the index of the cell or cells you’re interested in. For example, if you want to access the value of the cell in row 1, column 4, you can use:
## show value at row 1, col 4
df[1, 4]
## [1] 199502
Because data frames have column names (the variable names in our data
set), we can also refer to them by name. The fourth column is the
student date of birth variable, x1stdob. Using that instead of 4
(notice the quotation marks ""):
## show value at row 1, x1stdob column
df[1, "x1stdob"]
## [1] 199502
If we want to see more than one column, we can put the names in a
concatenated vector using the c() function:
## show values at row 1, stu_id & x1stdob column
df[1, c("stu_id", "x1stdob")]
## stu_id x1stdob
## 1 10001 199502
So far, we’ve not assigned these results to anything, so they’ve just printed to the console. However, we can assign them to a new object. If we want to slice our data so that we only have selected columns, we can leave the rows section blank (meaning we want all rows) and include all the columns we want to keep in our new data frame object.
## -----------------
## select
## -----------------
## select columns we need and assign to new object
df_tmp <- df[, c("stu_id", "x1stuedexpct", "x1paredexpct", "x1region")]
## show 10 rows
head(df_tmp, n = 10)
## stu_id x1stuedexpct x1paredexpct x1region
## 1 10001 8 6 2
## 2 10002 11 6 1
## 3 10003 10 10 4
## 4 10004 10 10 3
## 5 10005 6 10 3
## 6 10006 10 8 3
## 7 10007 8 11 1
## 8 10008 8 6 1
## 9 10009 11 11 3
## 10 10010 8 6 1
To conditionally change a variable, we’ll once again use the bracket notation to target our changes. This time, however, we do a couple of things differently:
<rows> part of the bracketAs before, we need to account for the fact that our two expectation
variables, x1stuedexpct and x1paredexpct, have values that need to
be converted to NA: -8, -9, and 11. See the first data
wrangling lesson for the rationale behind these changes.
First, let’s look at the unique values using the table()
function. So that we see any missing values, we’ll include an extra argument:
## -----------------
## mutate
## -----------------
## see unique values for student expectation
table(df_tmp$x1stuedexpct, useNA = "ifany")
##
## -8 1 2 3 4 5 6 7 8 9 10 11
## 2059 93 2619 140 1195 115 3505 231 4278 176 4461 4631
## see unique values for parental expectation
table(df_tmp$x1paredexpct, useNA = "ifany")
##
## -9 -8 1 2 3 4 5 6 7 8 9 10 11
## 32 6715 55 1293 149 1199 133 4952 76 3355 37 3782 1725
Notice that we use a dollar sign, $, to call the column name
directly. Unlike with the tidyverse, we cannot just use the column
name. Base R will look for that column name not as a column in a data
frame, but as its own object. It probably won’t find it (or worse,
you’ll have another object in memory that it will find and you’ll get
the wrong thing!).
Remember how data.frames are special matrices? One of the special
features is that you can use the $ sign with the column name as a
short cut or double square brackets without the comma.
## each version pulls the column of data for student expectations
## TRUE == 1, so if the mean of all values == 1, then all are TRUE
mean(df_tmp$x1stuedexpct == df_tmp[, "x1stuedexpct"]) == 1
## [1] TRUE
mean(df_tmp$x1stuedexpct == df_tmp[["x1stuedexpct"]]) == 1
## [1] TRUE
Back to replacing our missing values with NA…
The conditions we care about are when df_tmp$x1stuedexpct == -8, for
example. Using that condition in the row section of the square
bracket, we can replace only what we want.
## replace student expectation values
df_tmp$x1stuedexpct[df_tmp$x1stuedexpct == -8] <- NA
df_tmp$x1stuedexpct[df_tmp$x1stuedexpct == 11] <- NA
## replace parent expectation values
df_tmp$x1paredexpct[df_tmp$x1paredexpct == -8] <- NA
df_tmp$x1paredexpct[df_tmp$x1paredexpct == -9] <- NA
df_tmp$x1paredexpct[df_tmp$x1paredexpct == 11] <- NA
What each of these lines says is (first one for example): In the
data.frame df_tmp, replace the value in x1stuedexpct — where the
value of df_tmp$x1stuedexpct is -8 — with NA
As less convoluted way of saying this might be (more generally stated): Where the value in column A equals X, replace the value in column A with Y.
Let’s confirm using table() again. The values that were in -8,
-9, and 11 should now be summed under NA.
## see unique values for student expectation (confirm changes)
table(df_tmp$x1stuedexpct, useNA = "ifany")
##
## 1 2 3 4 5 6 7 8 9 10 <NA>
## 93 2619 140 1195 115 3505 231 4278 176 4461 6690
## see unique values for parental expectation (confirm changes)
table(df_tmp$x1paredexpct, useNA = "ifany")
##
## 1 2 3 4 5 6 7 8 9 10 <NA>
## 55 1293 149 1199 133 4952 76 3355 37 3782 8472
Adding a new variable to our data frame is just like modifying an
existing column. The only difference is that instead of putting an
existing column name after the first $ sign, we’ll
make up a new name. This tells R to add a new column to our data
frame.
As with the tidyverse version, we’ll use the ifelse() function to
create a new variable that is the higher of student or parental
expectations.
## add new column
df_tmp$high_expct <- ifelse(df_tmp$x1stuedexpct > df_tmp$x1paredexpct, # test
df_tmp$x1stuedexpct, # if TRUE
df_tmp$x1paredexpct) # if FALSE
## show first 10 rows
head(df_tmp, n = 10)
## stu_id x1stuedexpct x1paredexpct x1region high_expct
## 1 10001 8 6 2 8
## 2 10002 NA 6 1 NA
## 3 10003 10 10 4 10
## 4 10004 10 10 3 10
## 5 10005 6 10 3 10
## 6 10006 10 8 3 10
## 7 10007 8 NA 1 NA
## 8 10008 8 6 1 8
## 9 10009 NA NA 3 NA
## 10 10010 8 6 1 8
Again, our “ocular test” shows that this doesn’t handle
NA values correctly. Look at student 10002 in the second row:
while the student doesn’t have an expectation (or said “I don’t
know”), the parent does. However, our new variable records NA. Let’s
fix it with this test:
If
high_expctis missing andx1stuedexpctis not missing, replace with that; otherwise replace with itself (leave alone). Repeat, but forx1paredexpct. If stillNA, then we can assume both student and parent expectations were missing.
Translating the bold words to R code:
is.na()&!is.na() (! means NOT)we get:
## correct for NA values
## NB: We have to include [is.na(df_tmp$high_expct)] each time so that
## everything lines up
## step 1 student
df_tmp$high_expct[is.na(df_tmp$high_expct)] <- ifelse(
## test
!is.na(df_tmp$x1stuedexpct[is.na(df_tmp$high_expct)]),
## if TRUE do this...
df_tmp$x1stuedexpct[is.na(df_tmp$high_expct)],
## ... else do that
df_tmp$high_expct[is.na(df_tmp$high_expct)]
)
## step 2 parent
df_tmp$high_expct[is.na(df_tmp$high_expct)] <- ifelse(
## test
!is.na(df_tmp$x1paredexpct[is.na(df_tmp$high_expct)]),
## if TRUE do this...
df_tmp$x1paredexpct[is.na(df_tmp$high_expct)],
## ... else do that
df_tmp$high_expct[is.na(df_tmp$high_expct)]
)
That’s a lot of text! What’s happening is that we are trying to replace a vector of values with another vector of values, which need to line up and be the same length. That’s why we have
## what we'll use to replace when TRUE
df_tmp$x1stuedexpct[is.na(df_tmp$high_expct)]
When our high_expct column has missing values, we want to replace
with non-missing x1stuedexpct values in the same row. That means
we also need to subset that column to only include values in rows that
have missing high_expct values. Because we must do this each time,
our script gets pretty long and unwieldy.
Let’s check to make sure it worked as intended.
## show first 10 rows
head(df_tmp, n = 10)
## stu_id x1stuedexpct x1paredexpct x1region high_expct
## 1 10001 8 6 2 8
## 2 10002 NA 6 1 6
## 3 10003 10 10 4 10
## 4 10004 10 10 3 10
## 5 10005 6 10 3 10
## 6 10006 10 8 3 10
## 7 10007 8 NA 1 8
## 8 10008 8 6 1 8
## 9 10009 NA NA 3 NA
## 10 10010 8 6 1 8
Looking at the second observation again, it looks like we’ve fixed our
NA issue. Looking at rows 7 and 9, it seems like those situations
are correctly handled as well.
Let’s check the counts of our new variable:
## -----------------
## filter
## -----------------
## get summary of our new variable
table(df_tmp$high_expct, useNA = "ifany")
##
## 1 2 3 4 5 6 7 8 9 10 <NA>
## 71 2034 163 1282 132 4334 191 5087 168 6578 3463
Since we’re not going to use the missing values (we really can’t, even if we wanted to do so), we’ll drop those observations from our data frame.
As when we selected columns above, we’ll use the square brackets
notation. As with dplyr’s filter(), we want to filter in what we
want. We set this condition before the comma in the square
brackets. Because we want all the columns, we leave the space after
the comma blank.
## filter in values that aren't missing
df_tmp <- df_tmp[!is.na(df_tmp$high_expct),]
## show first 10 rows
head(df_tmp, n = 10)
## stu_id x1stuedexpct x1paredexpct x1region high_expct
## 1 10001 8 6 2 8
## 2 10002 NA 6 1 6
## 3 10003 10 10 4 10
## 4 10004 10 10 3 10
## 5 10005 6 10 3 10
## 6 10006 10 8 3 10
## 7 10007 8 NA 1 8
## 8 10008 8 6 1 8
## 10 10010 8 6 1 8
## 11 10011 8 6 3 8
It looks like we’ve dropped the rows with missing values in our new
variable (or, more technically, kept those without missing
values). Since we haven’t removed rows until now, we can compare the
number of rows in the original data frame, df, to what we have
now.
## is the original # of rows - current # or rows == NA in count?
nrow(df) - nrow(df_tmp)
## [1] 3463
Comparing the difference, we can see it’s the same as the number of missing values in our new column. While not a formal test, it does support what we expected (in other words, if the number were different, we’d definitely want to go back and investigate).
Now we’re ready to get the average of expectations that we need. For
an overall average, we can just use the mean() function.
## -----------------
## summarize
## -----------------
## get average (without storing)
mean(df_tmp$high_expct)
## [1] 7.272705
Overall, we can see that students and parents have high postsecondary expectations on average: to earn some graduate credential beyond a bachelor’s degree. However, this isn’t what we want. We want the values across census regions.
## check our census regions
table(df_tmp$x1region, useNA = "ifany")
##
## 1 2 3 4
## 3128 5312 8177 3423
We’re not missing any census data, which is good. To calculate our
average expectations, we need to use the aggregate function. This
function allows to compute a FUNction by a group. We’ll use it to
get our summary.
## get average (assigning this time)
df_tmp <- aggregate(df_tmp["high_expct"], # var of interest
by = list(region = df_tmp$x1region), # by group
FUN = mean) # function to run
## show
df_tmp
## region high_expct
## 1 1 7.389066
## 2 2 7.168110
## 3 3 7.357833
## 4 4 7.125329
Success! Expectations are similar across the country, but not the same by region.
As our final step, we’ll arrange our data frame from highest to lowest
(descending). For this, we’ll use sort() and the decreasing option.
## -----------------
## arrange
## -----------------
## arrange from highest expectations (first row) to lowest
df_tmp$high_expct <- sort(df_tmp$high_expct, decreasing = TRUE)
## show
df_tmp
## region high_expct
## 1 1 7.389066
## 2 2 7.357833
## 3 3 7.168110
## 4 4 7.125329
We can use this new data frame as a table in its own right or to make
a figure. For now, however, we’ll simply save it using the opposite of
read.csv() — write.csv() — which works like writeRDS() we’ve
used before.
## write with useful name
write.csv(df_tmp, file.path(dat_dir, "high_expct_mean_region.csv"))
And with that, we’ve met our task: we can show average educational expectations by region. To be very precise, we can show the higher of student and parental educational expectations among those who answered the question by region. This caveat doesn’t necessarily make our analysis less useful, but rather sets its scope. Furthermore, we’ve kept our original data as is (we didn’t overwrite it) for future analyses while saving the results of this analysis for quick reference.