Get bottom rows of tall array
Create a tall table and preview the bottom few rows of data.
Create a tall table for the airlinesmall.csv data set. Select a subset of the variables to work with. Use tail to extract the last few rows of data.
varnames = {'Year','Month','ArrDelay','DepDelay','UniqueCarrier'};
ds = datastore('airlinesmall.csv','TreatAsMissing','NA',...
'SelectedVariableNames',varnames);
T = tall(ds)
T =
M×5 tall table
Year Month ArrDelay DepDelay UniqueCarrier
____ _____ ________ ________ _____________
1987 10 8 12 'PS'
1987 10 8 1 'PS'
1987 10 21 20 'PS'
1987 10 13 12 'PS'
1987 10 4 -1 'PS'
1987 10 59 63 'PS'
1987 10 3 -2 'PS'
1987 10 11 -1 'PS'
: : : : :
: : : : :
tt = tail(T)
tt =
M×5 tall table
Year Month ArrDelay DepDelay UniqueCarrier
____ _____ ________ ________ _____________
? ? ? ? ?
? ? ? ? ?
? ? ? ? ?
: : : : :
: : : : :
Collect the results into memory to view the data.
last_rows = gather(tt)
Evaluating tall expression using the Local MATLAB Session:
- Pass 1 of 1: Completed in 0 sec
Evaluation completed in 1 sec
last_rows =
Year Month ArrDelay DepDelay UniqueCarrier
____ _____ ________ ________ _____________
2008 12 14 1 'DL'
2008 12 -8 -1 'DL'
2008 12 1 9 'DL'
2008 12 -8 -4 'DL'
2008 12 15 -2 'DL'
2008 12 -15 -1 'DL'
2008 12 -12 1 'DL'
2008 12 -1 11 'DL'
Preview the last 20 rows of data in a tall table.
Create a tall table for the airlinesmall.csv data set. Select a subset of the variables to work with, and treat 'NA' values as missing data so that datastore replaces them with NaN values. Use tail to view the last 20 rows of data.
varnames = {'Year','Month','ArrDelay','DepDelay','UniqueCarrier'};
ds = datastore('airlinesmall.csv','TreatAsMissing','NA',...
'SelectedVariableNames',varnames);
T = tall(ds)
T =
M×5 tall table
Year Month ArrDelay DepDelay UniqueCarrier
____ _____ ________ ________ _____________
1987 10 8 12 'PS'
1987 10 8 1 'PS'
1987 10 21 20 'PS'
1987 10 13 12 'PS'
1987 10 4 -1 'PS'
1987 10 59 63 'PS'
1987 10 3 -2 'PS'
1987 10 11 -1 'PS'
: : : : :
: : : : :
tt = tail(T,20)
tt =
M×5 tall table
Year Month ArrDelay DepDelay UniqueCarrier
____ _____ ________ ________ _____________
? ? ? ? ?
? ? ? ? ?
? ? ? ? ?
: : : : :
: : : : :
Collect the results into memory to view the data.
b20 = gather(tt)
Evaluating tall expression using the Local MATLAB Session:
- Pass 1 of 1: Completed in 1 sec
Evaluation completed in 1 sec
b20 =
Year Month ArrDelay DepDelay UniqueCarrier
____ _____ ________ ________ _____________
2008 12 0 -4 'CO'
2008 12 -16 13 'CO'
2008 12 17 -3 'CO'
2008 12 3 -5 'CO'
2008 12 2 6 'DL'
2008 12 6 -2 'DL'
2008 12 37 35 'DL'
2008 12 -1 -6 'DL'
2008 12 39 12 'DL'
2008 12 -3 -6 'DL'
2008 12 -6 -1 'DL'
2008 12 -2 1 'DL'
2008 12 14 1 'DL'
2008 12 -8 -1 'DL'
2008 12 1 9 'DL'
2008 12 -8 -4 'DL'
2008 12 15 -2 'DL'
2008 12 -15 -1 'DL'
2008 12 -12 1 'DL'
2008 12 -1 11 'DL'
X — Input arrayInput array, specified as a tall array.
Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical | table | cell | categorical | datetime | duration | calendarDuration
k — Number of rows to extractNumber of rows to extract, specified as a positive scalar integer.
If the tall array has fewer than k rows, then tail returns
the entire array.
Y — Requested rowsRequested rows, returned as an unevaluated tall array. To calculate Y and
bring it into memory, use gather(Y). For more information,
see Deferred Evaluation of Tall Arrays.
If you are unsure whether the result returned by gather(X) will
fit in memory, then use gather(head(X)) or gather(tail(X)).
These commands still fully evaluate the tall array X,
but only a small subset of the result is returned in memory.