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| all(x) | are all the logicals (i.e. x) true? |
| anova(x,y) | Tests is the regressions x or y are significantly different from one another. |
| any(x) | are any of the logicals (i.e. x) true? |
| assign(x,value,...) | I looked for months for this function, allows the use of paste() to create variables |
| attach.all() | Like attach, but it overwrites the data - has a dialogue box to prompt for overwriting. In the arm package. See Custom functions for the code. |
| axis(side,...) | Adds an axis to a plot, you can specify your own scale, which is nice when you don't want R to decide what labels to print. |
| by() | Very useful function that applies a function to certain levels of a factor. |
| class() | Returns the class of an object or variable. |
| colSums(x); rowSums(); colMeans(); rowMeans() | Sum by column and rows. apply(x,2,sum) does sums, too. |
| contrasts() <- contr.treatment() | Specifies the number of contrasts to make for a variable. After this is run, the variables can be put in a regression model. The contr.treatment specifies dummy coding for each category. |
| contrasts(age.f) <- contr.treatment(4, base = 2) | Re-specifies the reference categories, in the above case, 2 is the reference category and 4 is the number of categories. |
| CrossTable() | In the package "gmodels." Provides very nice crosstabs in R, with a nice, fixed-width format for the output. Can calculate proportions by row and/or columns. Very useful function. |
| C(x,base=1) | Sets the contrasts attribute associated with a factor - especially useful for turning a vector into a factor, with custom factor levels: this is a handy way to respecify the base category in a regression model. |
| get("characterstring") | Use this function to get a variable named with this character string. This is useful for passing a character string, which is the name of a variable, into a dataset and then attaching a dataframe and using get() to get the values of the variable with the name specified. |
| ifelse(conditional,valtrue,valfalse) | A short form of an if() else loop - very handy |
| ifelse(condition,T,F) | Condensed if-else statement, where T F are the return values. Can be nested. |
| install.packages("NAME",dependencies=TRUE,repos="http://cran.cnr.berkeley.edu/") | Download a package and install with dependencies. |
| jitter() | Add numbers around data points to expand a plot. |
| lapply(data.frame,function) | Applies a function to all the elements in a data frame. |
| latex() | A very flexible method of generating latex tables. Part of the Hmisc package. LOTS of customizations. |
| lm(write ~ I(age4 == 1) + I(age == 3) + I(age4 == 4)) | Another way of specifying the base category in regression models in R (2 is the base in this example) |
| ok= !is.na (x+y+z); clean=as.data.frame(cbind(x,y,z)[ok,]) | Creates an index of listwise deletion, you can filter the data on the ok index to remove the listwise cases. |
| paste(x,y,...) | Concatenates x and y, etc. as characters. Can be useful for generating patterns. |
| pR2 | Pseudo R2 for logits, etc, in pscl package |
| recode() {car package} | Recodes a numeric vector, character vector, or factor according to simple recode specifications. |
| relevel(x$y,ref="NAME") | Reorders a variable to make "NAME" the reference level |
| rm(list=ls()) | Removes all objects from the environment |
| sample() | Generate random integers |
| score.items() | in library(psych) Cronbach's alphas, variance and reliability in scales |
| source() | Reads in an R script from another file. |
| split() | Splits a data frame into vectors |
| split(x,f) | splits x into the categories defined by f, if you want only one category of f then use split(x,f)$CAT |
| str() | Structure of the object. This is a very helpful function that lets you figure out how an object is structured. |
| toupper(); tolower() | To upper case; to lower case. |
| unclass() | Removes the class attribute from an object. Very handy when you're trying to print the results of a regression. |
| unique() | This returns the unique values of a vector. Very useful for dumping duplicate cases. |
| x[-c(1,2,3),] | Remove multiple rows (or columns). |
| x[,drop=TRUE] | Drops the unused levels of a factor. factor(x) also works. |
| x%in%y | tests each element of x for membership in y |
| xtable() | A quick method to generate latex tables. Not nearly as flexible as Hmisc:latex, but easier. Part of the xtable package. |
