Computing on columns the data.table way

R'de data.table ile Veri İşleme

Matt Dowle, Arun Srinivasan

Instructors, DataCamp

Computing on columns

Since columns can be referred to as variables, you can compute directly on them in j

# Compute mean of duration column using the data.table way
ans <- batrips[, mean(duration)]

1131.967

# Compute mean of duration column using the data.frame way
ans <- mean(batrips[, "duration"])

1131.967
R'de data.table ile Veri İşleme

Computing on rows and columns

Combining i and j is straightforward

# Compute mean of duration column for "Japantown" start station
batrips[start_station == "Japantown", mean(duration)]

2464.331
R'de data.table ile Veri İşleme

Special symbol .N in j

  • .N can be used in j as well
  • Particularly useful to get the number of rows after filtering in i
# How many trips started from "Japantown"?
batrips[start_station == "Japantown", .N]

902

# Compare this to the data.frame way
nrow(batrips[batrips$start_station == "Japantown", ])

902
R'de data.table ile Veri İşleme

Let's practice!

R'de data.table ile Veri İşleme

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