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Suppose that I have a data frame that has a column called C. C has many levels that only occur once. How would I rename all of the levels that occur only once with a new level (called z)?
A B C
a a a
a b b
a a c
a b d
a b a
The above would turn into:
A B C
a a a
a b z
a a z
a b z
a b a
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Groupby Function in R – group_by is used to group the dataframe in R. Dplyr package in R is provided with group_by () function which groups the dataframe by multiple columns with mean, sum and other functions like count, maximum and minimum.
The number of groups may be reduced, based on conditions. dataframe attributes are preserved during data filter. Any dataframe column in the R programming language can be referenced either through its name df$col-name or using its index position in the dataframe df [col-index].
Two of the most common tasks that you’ll perform in data analysis are grouping and summarizing data. Fortunately the dplyr package in R allows you to quickly group and summarize data. This tutorial provides a quick guide to getting started with dplyr. Before you can use the functions in the dplyr package, you must first load the package:
Cells in dataframe can contain missing values or NA as its elements, and they can be verified using is.na () method in R language. Column values can be subjected to constraints to filter and subset the data. The values can be mapped to specific occurrences or within a range.
What about this (assuming your data is df)?
levels(df[,3])[table(df[,3])==1] <- "z"
df
A B C
1 a a a
2 a b z
3 a a z
4 a b z
5 a b a
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