Description Usage Arguments Details Value Feature selection Using reduced dimensions Using alternative Experiments Author(s) References See Also Examples

Perform t-stochastic neighbour embedding (t-SNE) for the cells, based on the data in a SingleCellExperiment object.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | ```
calculateTSNE(x, ...)
## S4 method for signature 'ANY'
calculateTSNE(
x,
ncomponents = 2,
ntop = 500,
subset_row = NULL,
scale = FALSE,
transposed = FALSE,
perplexity = NULL,
normalize = TRUE,
theta = 0.5,
num_threads = NULL,
...,
external_neighbors = FALSE,
BNPARAM = KmknnParam(),
BPPARAM = SerialParam()
)
## S4 method for signature 'SummarizedExperiment'
calculateTSNE(x, ..., exprs_values = "logcounts")
## S4 method for signature 'SingleCellExperiment'
calculateTSNE(
x,
...,
pca = is.null(dimred),
exprs_values = "logcounts",
dimred = NULL,
n_dimred = NULL
)
runTSNE(x, ..., altexp = NULL, name = "TSNE")
``` |

`x` |
For For |

`...` |
For the For |

`ncomponents` |
Numeric scalar indicating the number of t-SNE dimensions to obtain. |

`ntop` |
Numeric scalar specifying the number of features with the highest variances to use for dimensionality reduction. |

`subset_row` |
Vector specifying the subset of features to use for dimensionality reduction. This can be a character vector of row names, an integer vector of row indices or a logical vector. |

`scale` |
Logical scalar, should the expression values be standardized? |

`transposed` |
Logical scalar, is |

`perplexity` |
Numeric scalar defining the perplexity parameter, see |

`normalize` |
Logical scalar indicating if input values should be scaled for numerical precision, see |

`theta` |
Numeric scalar specifying the approximation accuracy of the Barnes-Hut algorithm, see |

`num_threads` |
Integer scalar specifying the number of threads to use in |

`external_neighbors` |
Logical scalar indicating whether a nearest neighbors search should be computed externally with |

`BNPARAM` |
A BiocNeighborParam object specifying the neighbor search algorithm to use when |

`BPPARAM` |
A BiocParallelParam object specifying how the neighbor search should be parallelized when |

`exprs_values` |
Integer scalar or string indicating which assay of |

`pca` |
Logical scalar indicating whether a PCA step should be performed inside |

`dimred` |
String or integer scalar specifying the existing dimensionality reduction results to use. |

`n_dimred` |
Integer scalar or vector specifying the dimensions to use if |

`altexp` |
String or integer scalar specifying an alternative experiment containing the input data. |

`name` |
String specifying the name to be used to store the result in the |

The function `Rtsne`

is used internally to compute the t-SNE.
Note that the algorithm is not deterministic, so different runs of the function will produce differing results.
Users are advised to test multiple random seeds, and then use `set.seed`

to set a random seed for replicable results.

The value of the `perplexity`

parameter can have a large effect on the results.
By default, the function will set a “reasonable” perplexity that scales with the number of cells in `x`

.
(Specifically, it is the number of cells divided by 5, capped at a maximum of 50.)
However, it is often worthwhile to manually try multiple values to ensure that the conclusions are robust.

If `external_neighbors=TRUE`

, the nearest neighbor search step will use a different algorithm to that in the `Rtsne`

function.
This can be parallelized or approximate to achieve greater speed for large data sets.
The neighbor search results are then used for t-SNE via the `Rtsne_neighbors`

function.

If `dimred`

is specified, the PCA step of the `Rtsne`

function is automatically turned off by default.
This presumes that the existing dimensionality reduction is sufficient such that an additional PCA is not required.

For `calculateTSNE`

, a numeric matrix is returned containing the t-SNE coordinates for each cell (row) and dimension (column).

For `runTSNE`

, a modified `x`

is returned that contains the t-SNE coordinates in `reducedDim(x, name)`

.

This section is relevant if `x`

is a numeric matrix of (log-)expression values with features in rows and cells in columns;
or if `x`

is a SingleCellExperiment and `dimred=NULL`

.
In the latter, the expression values are obtained from the assay specified by `exprs_values`

.

The `subset_row`

argument specifies the features to use for dimensionality reduction.
The aim is to allow users to specify highly variable features to improve the signal/noise ratio,
or to specify genes in a pathway of interest to focus on particular aspects of heterogeneity.

If `subset_row=NULL`

, the `ntop`

features with the largest variances are used instead.
We literally compute the variances from the expression values without considering any mean-variance trend,
so often a more considered choice of genes is possible, e.g., with scran functions.
Note that the value of `ntop`

is ignored if `subset_row`

is specified.

If `scale=TRUE`

, the expression values for each feature are standardized so that their variance is unity.
This will also remove features with standard deviations below 1e-8.

If `x`

is a SingleCellExperiment, the method can be applied on existing dimensionality reduction results in `x`

by setting the `dimred`

argument.
This is typically used to run slower non-linear algorithms (t-SNE, UMAP) on the results of fast linear decompositions (PCA).
We might also use this with existing reduced dimensions computed from *a priori* knowledge (e.g., gene set scores), where further dimensionality reduction could be applied to compress the data.

The matrix of existing reduced dimensions is taken from `reducedDim(x, dimred)`

.
By default, all dimensions are used to compute the second set of reduced dimensions.
If `n_dimred`

is also specified, only the first `n_dimred`

columns are used.
Alternatively, `n_dimred`

can be an integer vector specifying the column indices of the dimensions to use.

When `dimred`

is specified, no additional feature selection or standardization is performed.
This means that any settings of `ntop`

, `subset_row`

and `scale`

are ignored.

If `x`

is a numeric matrix, setting `transposed=TRUE`

will treat the rows as cells and the columns as the variables/diemnsions.
This allows users to manually pass in dimensionality reduction results without needing to wrap them in a SingleCellExperiment.
As such, no feature selection or standardization is performed, i.e., `ntop`

, `subset_row`

and `scale`

are ignored.

This section is relevant if `x`

is a SingleCellExperiment and `altexp`

is not `NULL`

.
In such cases, the method is run on data from an alternative SummarizedExperiment nested within `x`

.
This is useful for performing dimensionality reduction on other features stored in `altExp(x, altexp)`

, e.g., antibody tags.

Setting `altexp`

with `exprs_values`

will use the specified assay from the alternative SummarizedExperiment.
If the alternative is a SingleCellExperiment, setting `dimred`

will use the specified dimensionality reduction results from the alternative.
This option will also interact as expected with `n_dimred`

.

Note that the output is still stored in the `reducedDims`

of the output SingleCellExperiment.
It is advisable to use a different `name`

to distinguish this output from the results generated from the main experiment's assay values.

Aaron Lun, based on code by Davis McCarthy

van der Maaten LJP, Hinton GE (2008).
Visualizing High-Dimensional Data Using t-SNE.
*J. Mach. Learn. Res.* 9, 2579-2605.

`Rtsne`

, for the underlying calculations.

`plotTSNE`

, to quickly visualize the results.

1 2 3 4 5 6 | ```
example_sce <- mockSCE()
example_sce <- logNormCounts(example_sce)
example_sce <- runTSNE(example_sce)
reducedDimNames(example_sce)
head(reducedDim(example_sce))
``` |

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